Release protoc_plugin-21.1.2 (google#881)

Rename a local variable to avoid proto field name conflicts, re-gener…

…ate protos (google#869)

- Rename a local variable to avoid proto field name conflicts.

  This fixes an issue we're seeing with the latest version of
  `package:protoc_plugin` and the dartpad proto definitions.

- Re-generate descriptor protos.

- Update CI config to re-run publishing when labels change.

Release protobuf-3.1.0, protoc_plugin-21.1.0 (google#868)

Release protobuf-3.1.0, protoc_plugin-21.1.0 (google#868)

Remove protoc_plugin exe from repo, update .gitignore (google#851)

Also bump version number as I've retracted the last release.

Fixes google#847.

Fix missing protobuf import in grpc files (google#845)

Fixes google#844.

Release protobuf-3.0.0, protoc_plugin-21.0.0 (google#843)

Release protobuf-3.0.0, protoc_plugin-21.0.0 (google#843)

Release protobuf-2.1.0, protoc_plugin-20.0.1 (google#677)

Release protobuf-2.1.0, protoc_plugin-20.0.1 (google#677)