Relands #17489 with a fix for the unit test flake.
The previous unit test relied on the new instance not being created at the same memory address, which isn't guaranteed.
Seems to have triggered flaky failures on the Windows bot since landing.
Example failure:
[ RUN ] PluginRegistrarTest.ManagerRemovesOnDestruction
c:\b\s\w\ir\cache\builder\src\flutter\shell\platform\common\cpp\client_wrapper\plugin_registrar_unittests.cc(149): error: Expected: (manager->GetRegistrar<PluginRegistrar>(dummy_registrar_handle)) != (first_wrapper), actual: 000002400A90E3D0 vs 000002400A90E3D0
This reverts commit faf44fed5a5913dcbeebd7ead8e3933a5e72a6fc.
This makes two changes:
- Adds a way to register a callback for when a FlutterDesktopPluginRegistrarRef is destroyed, and implements the logic to call it in the Windows and Linux embeddings.
- Adds a class to the C++ wrapper that handles making a singleton owning PluginRegistrar wrappers, and destroying them when the underlying reference goes away, to avoid needing that boilerplate code in every plugin's source.
Fixes https://github.com/flutter/flutter/issues/53496
Adds StandardMethodCodec support to the C++ client wrapper. This makes it
substantially easier to add Windows and Linux support for existing plugins, as
StandardMethodCodec is the default plugin protocol.
Fixesflutter/flutter#30670
Does not include extensibility for the codec, which will be added later.
Changes include:
- File structure
- Header guards
- Include paths
- Namespaces
- Integration with the engine's GN build
- Conversion from jsoncpp to rapidjson
- Style and clang-format adjustment to match engine repository
