[flutter_tools] Add ProjectExtensionFinder and ExtensionKernelCompiler - #194772

…onfig validation

- Acquire an exclusive lockfile (.dill.lock) via FileSystemLocking.runLocked and atomically rename temporary .dill.tmp and .d.tmp outputs in ExtensionKernelCompiler.compile.
- Ensure --extensions does not bypass FLUTTER_NO_EXTENSIONS=1 or enable tool extensions when the feature flag is disabled.
- Validate ExtensionPackageConfig.entrypoint against path traversal and filter platform template queries by requested custom platforms.
- Make FeatureFlags required on ExtensionManager and Artifacts required on ExtensionKernelCompiler, and refresh ExtensionBuildManager.getBuildTargets when new extension connections initialize.

… Isolate.spawnUri support

- Scope this branch to the ExtensionPackageConfig manifest model in flutter_tools_core, Isolate.spawnUri entrypoint support in flutter_tools_extension and flutter_tools_extension_linux_prototype, and ExtensionConnection.spawnUri in extension_discovery.dart.
- Split safe mode, ProjectExtensionFinder / ExtensionKernelCompiler, and dynamic discovery wiring into separate stacked PRs.

- Add ProjectExtensionFinder to discover tool extensions via package:extension_discovery and extension/flutter_tools/config.yaml filtered to direct project and Pub workspace dependencies.
- Add ExtensionKernelCompiler to compile extension entrypoints to .dill Kernel files with shared PUB_CACHE and workspace caching, --depfile invalidation, exclusive lockfiles, and atomic temporary file renames.

…1c-finder-and-compiler

…-project-discovery

…1c-finder-and-compiler

… ExtensionKernelCompiler

…ty, and remove handshake timeout

…1c-finder-and-compiler

…1c-finder-and-compiler

…roject-discovery

# Conflicts:
#	packages/flutter_tools/lib/src/experimental/extension_discovery.dart
#	packages/flutter_tools/packages/flutter_tools_core/lib/flutter_tools_core.dart
#	packages/flutter_tools/packages/flutter_tools_extension/lib/src/protocol_base/provider.dart

…1c-finder-and-compiler

# Conflicts:
#	packages/flutter_tools/test/general.shard/extension_protocol/extension_discovery_test.dart

… ExtensionConnection

- Mark `ExtensionConnection.spawn` as `@visibleForTesting` and suppress the
  transitional use in `ExtensionManager.initialize()` until flutter#194774.
- Add `ExtensionJsonParsing.stringSet` for parsing sets of unique strings,
  optionally trimming and rejecting empty entries.
- Require a non-empty `services` list in `ExtensionPackageConfig`, use
  `stringSet` for all list fields, accept `Map<String, Object?>` in
  `fromMap`, and document string identifier conventions.

Part of flutter#190755

…1c-finder-and-compiler

…onPackageConfig changes

… clean up ignore comment

- Use a comma instead of a second `//` in the transitional suppression in
  `ExtensionManager.initialize()`:
  `// ignore: invalid_use_of_visible_for_testing_member, transitional until flutter#194774.`
- Drop `protocol_version` from `ExtensionPackageConfig`, its schema
  documentation, and the Linux prototype `config.yaml`. Protocol
  compatibility is governed by `package:flutter_tools_extension`
  dependency versions and no runtime protocol negotiation is performed.

Part of flutter#190755

…hase01c-finder-and-compiler

Follows the parent change that dropped protocol_version from ExtensionPackageConfig.

…nd trim config string lists

- Remove redundant `Isolate` type on initializing formal `this._isolate`.
- Trim `supportedPlatforms`, `services`, `buildTargets`, and `templates` in `ExtensionPackageConfig` constructor.

Part of flutter#190755

Use `getDartDataHome` from `package:dart_data_home` to resolve the shared extension cache directory in `ExtensionKernelCompiler` instead of manually inspecting OS-specific environment variables.

Reuses Pubspec.parse from package:pubspec_parse in ProjectExtensionFinder, ErrorHandlingFileSystem.deleteIfExists in ExtensionKernelCompiler, and shared test fixtures in extension_discovery_test.dart, while matching MemoryFileSystem style to the host platform in getDartDataHome tests instead of replacing path separators in production code.

…inder-and-compiler

# Conflicts:
#	packages/flutter_tools/pubspec.yaml
#	pubspec.yaml

… paths in extension_discovery_test

Construct root paths from `fs.currentDirectory.path` in the `_hostStyleMemoryFs()` tests so paths include a drive letter on `FileSystemStyle.windows` (`Windows tool_tests_general`).

Part of flutter#190755

… helpers

Use `.childDirectory(...)` chains instead of forward-slash relative paths in `_writeExtensionPackage` and `_writePackageConfig` so `MemoryFileSystem(style: FileSystemStyle.windows)` matches `extension.entrypointUri` on Windows.

Part of flutter#190755

…der-and-compiler

Require a non-empty `bin/cache/dart-sdk/revision` when resolving and validating cached extension `.dill` artifacts, recording `.dill.revision` stamps alongside compiled kernels instead of relying on archived SDK file timestamps.

Scope shared `$PUB_CACHE` `.dill` eligibility and cache keys to the extension's transitive dependency closure from `package_graph.json`, preserve `+` in sanitized version labels, delete stale depfiles when absent, map `ProcessException` and `FileSystemException` to `ExtensionCompileException`, and clarify `ProjectExtensionFinder` doc comments.

Escape backslashes (`\\`) and spaces (`\ `) when generating synthetic `.dill.d` depfiles in `extension_discovery_test.dart` (matching `dart compile kernel --depfile`) so `DepfileService.parse` preserves Windows separators instead of stripping single backslashes and triggering cache misses on `Windows tool_tests_general`.

Use `_hostStyleMemoryFs()` and host-rooted paths across the `DART_DATA_HOME` shared-cache tests so `getDartDataHome` (which resolves paths via `dart:io` for the host OS) does not emit drive-less `\data_home\...` paths onto a POSIX `MemoryFileSystem` on Windows. Normalize `_resolveDillTarget` outputs to `.absolute` in `ExtensionKernelCompiler` so `resolveDillFile` and `compile` always agree on an absolute path and `file://` URI even when `DART_DATA_HOME` is relative, and add an end-to-end `FileSystemStyle.windows` test covering discovery, compilation, cache reuse, and depfile invalidation.

Previous output:
```
00:38 +3476 ~2 -1: test/general.shard\extension_protocol\extension_discovery_test.dart: ExtensionKernelCompiler caches immutable PUB_CACHE extension under DART_DATA_HOME/flutter_tool_extensions/cache [E]
  Expected: non-empty
    Actual: []
  ProcessManager was told to execute [Artifact.engineDartBinary, compile, kernel, --packages=C:\workspace\app\.dart_tool\package_config.json, --output=C:\custom_data\flutter_tool_extensions\cache\hosted_ext-3.13.0-8b74fd2bc9ed87037574eae76663fef19c01ac996ea7daf939ea86e31ba9a48c.dill.tmp, --depfile=C:\custom_data\flutter_tool_extensions\cache\hosted_ext-3.13.0-8b74fd2bc9ed87037574eae76663fef19c01ac996ea7daf939ea86e31ba9a48c.dill.d.tmp, C:\home\test\.pub-cache\hosted\pub.dev\hosted_ext-1.2.3\bin\hosted_ext.dart] (in null) but the FakeProcessManager.list expected no more processes.

00:39 +3484 ~2 -2: test/general.shard\extension_protocol\extension_discovery_test.dart: ExtensionKernelCompiler scopes shared cache closure via package_graph.json and ignores compiling project package_config.json mtime [E]
  Expected: Uri:<%5Cdata_home%5Cflutter_tool_extensions%5C/cache/hosted_ext-3.13.0-0.0.pre-ec4da305df37ae2e66a44f9091c46d942e2068ef454eda13febcb087295840dc.dill>
    Actual: Uri:<file:///%5Cdata_home%5Cflutter_tool_extensions%5C/cache/hosted_ext-3.13.0-0.0.pre-ec4da305df37ae2e66a44f9091c46d942e2068ef454eda13febcb087295840dc.dill>
```

Current output:
```
+45: All tests passed!
```

Part of flutter#190755

…der-and-compiler

# Conflicts:
#	pubspec.yaml

…der-and-compiler

…ache

Simplifies `ExtensionKernelCompiler` to cache compiled extension `.dill` snapshots in `<workspace>/.dart_tool/flutter_tools/extensions/<package>/extension.dill` alongside `extension.dill.d` and `extension.dill.stamp`, dropping the `$DART_DATA_HOME` shared cache tier, `pubspec.lock` and `package_graph.json` parsing, and the `package:dart_data_home` dependency.

Records the whole-second compilation start timestamp (`compiledAt`) before hashing `.dart_tool/package_config.json` or invoking `dart compile kernel`, commits `.d`, `.dill`, and `.stamp` in order with an explicit `buildToken` (`CompiledExtensionKernel`), and invalidates whenever any depfile source input has a modification timestamp at or after `compiledAt` so edits saved mid-compile invalidate cached snapshots.

Part of flutter#190755