[objective_c] Link Foundation in the native support library - #3782

Description

The ObjC bindings load classes through their OBJC_CLASS_$_Foo symbols, resolved via the objective_c.dylib handle, and fall back to objc_getClass when that lookup throws (#3344). The native support library is linked with -undefined dynamic_lookup and no frameworks, so it only depends on libSystem:

$ otool -L objective_c.framework/objective_c
	@rpath/objective_c.framework/objective_c
	/usr/lib/libSystem.B.dylib

As a result dlsym can never find a built-in Foundation class through that handle, and the first use of every Foundation class in package:objective_c (NSArray, NSString, ...) throws an ArgumentError that getClass catches before falling back:

ArgumentError (Invalid argument(s): Couldn't resolve native function 'OBJC_CLASS_$_NSArray' in 'package:objective_c/objective_c.dylib' : Failed to lookup symbol 'OBJC_CLASS_$_NSArray': dlsym(0x90466c40, OBJC_CLASS_$_NSArray): symbol not found.

The result is still correct, but a debugger that breaks on all exceptions stops at app startup on any Flutter app that uses path_provider (via path_provider_foundation), with no way to skip just this exception.

This PR links the support library against Foundation, so these symbols resolve through the dylib's dependencies, to the same class pointers objc_getClass returns. The dylib's own classes (DOBJC*) still resolve as before, and the fallback is kept for other frameworks.

Related Issues

Follow-up to #3344 (which fixed #3338). There is no separate issue for this; happy to file one if preferred.

Testing

• Added a test in test/internal_test.dart that resolves OBJC_CLASS_$_NSArray through package:objective_c/objective_c.dylib and compares it with getClass('NSArray'). It fails on main with the ArgumentError above and passes with this change.
• Ran the macOS jobs of objective_c.yaml and ffigen.yml locally (macOS 27, Xcode 27.1, Flutter 3.47.9 / Dart 3.13.7):
  • pkgs/objective_c: dart format --set-exit-if-changed, flutter analyze --fatal-infos, the snippet check and dart test (152 tests) pass.
  • example/command_line: dart run lib/main.dart works.
  • example/flutter_app: flutter build macos, flutter build ios --no-codesign and xcodebuild analyze (warnings as errors) succeed. otool -L on the bundled objective_c.framework now lists Foundation for both macOS slices and iOS.
  • pkgs/ffigen: dart test gives the same result with and without this change: 901 passed, 1 failed (verify_bindings_test for sdk_variable_test.dart, a bindings diff from the Xcode 27.1 SDK).

Note: with the Xcode 27.1 SDK, test/generate_code_test.dart regenerates objective_c_bindings_generated.dart with a few new deprecated 27.0.0 annotations. That is unrelated to this change and not included.

PR Checklist

• I’ve reviewed the contributor guide and applied the relevant portions to this PR.
• I've run dart tool/ci.dart --all locally and resolved all issues identified. (It doesn't cover pkgs/objective_c or pkgs/ffigen, so I also ran their workflow jobs, see Testing. Everything passes except 4 swift2objc integration tests, whose expected output differs with the local Xcode 27.1 Swift, and the swift2objc apitool missing-export check. This PR doesn't touch swift2objc, which doesn't depend on objective_c.)
• All existing and new tests are passing. I added new tests to check the change I am making.
• The PR is actually solving the issue.
• I have updated CHANGELOG.md for the relevant packages.
• I have updated the pubspec package version if necessary.