fix(codegen): skip third-party components whose class is not linked

[YevheniiKotyrlo]

Summary:

Cherry-pick of react#59067 (acc0cca), without its test-file change, which edits a generate-artifacts-executor-test.js case this branch does not have.

The generated RCTThirdPartyComponentsProvider.mm builds its map from a dictionary literal of NSClassFromString results, so when a component's class is not linked into the app, the literal gets nil and the app aborts at launch:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSPlaceholderDictionary initWithObjects:forKeys:count:]: attempt to insert nil object from objects[1]'

On macOS this happens whenever a dependency's components have no macOS classes: codegen runs with -t ios, so their entries reach the macOS app's provider, and platforms: { macos: null } in react-native.config.js does not keep them out, since the disabled-library filter reads the ios entry. react-native-skia's macOS example aborts at launch this way on 0.81. The provider now maps component names to class names and registers only the classes the runtime has, as RCTModuleProvidersMM.template does for modules.

0.81-stable and 0.83-stable carry the same template, and this commit cherry-picks onto both without conflicts.

Test Plan:

• generate-artifacts-executor-test.js: its two RCTThirdPartyComponentsProvider.mm snapshots expect the new map. With main's template and generator they fail; with this change the file's 39 tests pass, here and on 0.83-stable with the commit cherry-picked.
• The provider generated for two components, compiled with Apple clang 21 (macOS 27) into a binary that links only one of their classes:
  • main: NSInvalidArgumentException … attempt to insert nil object from objects[1]
  • this change: registered components: LinkedComponent
• RNTester builds for macOS, iOS and visionOS (static linkage, Xcode 27), each compiling the provider the new template generates.
• yarn test-ci, yarn flow-check, yarn lint, yarn format-check and yarn constraints pass.

Not run here: the macOS core prebuild.

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