This allows rules_proto to supply a pre-built binary toolchain for protoc without needing any Bazel module supplied by the protocolbuffers maintainers.
Obviates the need for protobuf to be released to the BCR as in protocolbuffers/protobuf#16014
Allows the protocolbuffers team to stop caring about Bazel builds for external users, and to close associated bugs.

Next step in rules_proto supplying a toolchain that doesn't require users build protoc from sources.

It seems that Googlers aren't checking the same buildifier warnings in google3 that GitHub enforces, so the main branch was already red.
Fixing to green up my PR.

…or code users access