16945 Fixed FlutterPlugin.h doxygen. (cla: yes)

16947 doxygen tooling updates and doxygen for FlutterCodecs.h (cla: yes)

16948 Remove duplicate dependency on the Dart language model (cla: yes)

16949 Roll fuchsia/sdk/core/mac-amd64 from 8HrJn… to 6eF38… (cla: yes, waiting for tree to go green)

16950 documented fluttertexture.h (cla: yes)

16952 Roll fuchsia/sdk/core/linux-amd64 from vH9-3… to cXgMr… (cla: yes, waiting for tree to go green)