Generate docs of enums and rpc clients, some refactoring #1279

Job	Run time
format_analyze; linux; Dart 2.19.0; PKG: protobuf; `dart analyze lib`, `dart analyze test`	20s
format_analyze; linux; Dart dev; PKG: api_benchmark; `dart format --output=none --set-exit-if-cha...	30s
format_analyze; linux; Dart dev; PKG: benchmarks; `dart format --output=none --set-exit-if-change...	23s
mono_repo self validate	14s
format_analyze; linux; Dart dev; PKG: protobuf; `dart format --output=none --set-exit-if-changed ...	22s
format_analyze; linux; Dart dev; PKG: protoc_plugin; `dart format --output=none --set-exit-if-cha...	31s
run_tests; linux; Dart 2.19.0; PKG: protobuf; `dart test`	31s
run_tests; linux; Dart 2.19.0; PKG: protoc_plugin; `./../tool/setup.sh`, `make protos`, `dart test`	38s
run_tests; linux; Dart dev; PKG: protobuf; `dart test`	28s
run_tests; osx; Dart 2.19.0; PKG: protobuf; `dart test`	57s
run_tests; linux; Dart dev; PKG: protoc_plugin; `./../tool/setup.sh`, `make protos`, `dart test`	42s
run_tests; osx; Dart dev; PKG: protobuf; `dart test`	1m 1s
run_tests; windows; Dart 2.19.0; PKG: protobuf; `dart test`	52s
run_tests; windows; Dart dev; PKG: protobuf; `dart test`	44s
run_legacy_tests; linux; Dart 2.19.0; PKG: protoc_plugin; `./../tool/setup.sh`, `make protos`, `d...	36s
	8m 49s

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