[flutter_tools] Wire project extension discovery, lazy service filtering, and custom create platforms - #194774

…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.

…mode

- Add the global --[no-]extensions CLI flag and FLUTTER_NO_EXTENSIONS=1 environment variable to bypass tool extension discovery and isolate spawning.
- Make FeatureFlags required on ExtensionManager and wire isSafeMode through ToolDependencies.bootstrap and FlutterFeatureFlags.isEnabled.

- 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.

…-discovery-wiring

…ing, and custom create platforms

- Wire ProjectExtensionFinder and ExtensionKernelCompiler into ExtensionManager and ToolDependencies.bootstrap, and remove the static linuxExtensionEntryPoint from executable.dart.
- Add lazy requiredServices capability filtering to ExtensionManager.ensureInitialized across config, doctor, build, device, and template managers.
- Resolve package:<extension>/... template directories in ExtensionTemplateManager and support custom --platforms in flutter create.

…1c-finder-and-compiler

…-project-discovery

…afe-mode

…1c-finder-and-compiler

… ExtensionKernelCompiler

…1d-dynamic-discovery-wiring

# Conflicts:
#	packages/flutter_tools/lib/src/runner/flutter_command.dart

…review feedback

…re in config_test

…ty, and remove handshake timeout

…date top-level flag collection

- Remove isToolExtensionsEnabledOverride from runner.dart, ToolDependencies.bootstrap, and FlutterFeatureFlags, reading --[no-]extensions from globalResults in ConfigCommand and DoctorCommand.
- Consolidate top-level CLI flag collection and option token skipping in FlutterCommandRunner.

…1c-finder-and-compiler

…1d-dynamic-discovery-wiring

…nection.spawn @VisibleForTesting

…1d-dynamic-discovery-wiring

# Conflicts:
#	packages/flutter_tools/lib/src/experimental/extension_discovery.dart

…rt disable lifecycle

In _optionTokenCount, fall back to checking the root argParser when an
option is not found in the current subcommand parser. This ensures global
options with value arguments passed after a subcommand consume their
arguments properly rather than treating the value as a subcommand name.

Also add an assertion to ExtensionManager.disable() to ensure disable()
cannot be called after initialization has started.

Part of flutter#190755

…-discovery-wiring

… 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.

…1d-dynamic-discovery-wiring

# Conflicts:
#	packages/flutter_tools/lib/src/experimental/extension_manager.dart

…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

…1d-dynamic-discovery-wiring

…y' into ft-ext-phase01c-finder-and-compiler

…1d-dynamic-discovery-wiring

# Conflicts:
#	packages/flutter_tools/lib/src/experimental/extension_manager.dart
#	packages/flutter_tools/test/commands.shard/hermetic/tool_extensions_integration_test.dart
#	packages/flutter_tools/test/general.shard/extension_protocol/extension_manager_test.dart

Adds an explicit `trim` parameter to `stringSet` so trimming is no longer
implied by `rejectEmpty`. `ExtensionPackageConfig.fromMap` now passes
`trim: true` explicitly at each call site, and the doc comment describes
the trimming and empty element behavior.

Part of flutter#190755

…y' into ft-ext-phase01c-finder-and-compiler

…1d-dynamic-discovery-wiring

…-project-discovery

# Conflicts:
#	packages/flutter_tools/lib/src/experimental/extension_discovery.dart
#	packages/flutter_tools/test/general.shard/extension_protocol/extension_discovery_test.dart

…y' into ft-ext-phase01c-finder-and-compiler

…inder-and-compiler

…1d-dynamic-discovery-wiring

… ToolExtensionEntryPoint

…y' into ft-ext-phase01c-finder-and-compiler

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

…1d-dynamic-discovery-wiring

…for ExtensionPackageConfig API changes