Generate docs of enums and rpc clients, some refactoring #1274

Job	Run time
mono_repo self validate	14s
format_analyze; linux; Dart dev; PKG: api_benchmark; `dart format --output=none --set-exit-if-cha...	30s
format_analyze; linux; Dart dev; PKG: protobuf; `dart format --output=none --set-exit-if-changed ...	24s
format_analyze; linux; Dart dev; PKG: benchmarks; `dart format --output=none --set-exit-if-change...	21s
format_analyze; linux; Dart dev; PKG: protoc_plugin; `dart format --output=none --set-exit-if-cha...	32s
format_analyze; linux; Dart 2.19.0; PKG: protobuf; `dart analyze lib`, `dart analyze test`	22s
run_tests; linux; Dart 2.19.0; PKG: protobuf; `dart test`	27s
run_tests; linux; Dart dev; PKG: protobuf; `dart test`	26s
run_tests; linux; Dart 2.19.0; PKG: protoc_plugin; `./../tool/setup.sh`, `make protos`, `dart test`	40s
run_tests; linux; Dart dev; PKG: protoc_plugin; `./../tool/setup.sh`, `make protos`, `dart test`	39s
run_tests; osx; Dart 2.19.0; PKG: protobuf; `dart test`	45s
run_tests; osx; Dart dev; PKG: protobuf; `dart test`	55s
run_tests; windows; Dart 2.19.0; PKG: protobuf; `dart test`	37s
run_tests; windows; Dart dev; PKG: protobuf; `dart test`	39s
run_legacy_tests; linux; Dart 2.19.0; PKG: protoc_plugin; `./../tool/setup.sh`, `make protos`, `d...	32s
	8m 3s

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