The plugin name is an opaque string, but by convention they are maven-esqe artifact identifiers that follow a GitHub org/repo/plugin_name convention.
$ bazel query 'kind(proto_plugin,@build_stack_rules_proto//...)' --keep_going@build_stack_rules_proto//plugin/akka/akka-grpc:protoc-gen-akka-grpc
@build_stack_rules_proto//plugin/bufbuild:connect-es
@build_stack_rules_proto//plugin/bufbuild:es
@build_stack_rules_proto//plugin/builtin:closurejs
@build_stack_rules_proto//plugin/builtin:commonjs
@build_stack_rules_proto//plugin/builtin:cpp
@build_stack_rules_proto//plugin/builtin:csharp
@build_stack_rules_proto//plugin/builtin:java
@build_stack_rules_proto//plugin/builtin:objc
@build_stack_rules_proto//plugin/builtin:php
@build_stack_rules_proto//plugin/builtin:pyi
@build_stack_rules_proto//plugin/builtin:python
@build_stack_rules_proto//plugin/builtin:ruby
@build_stack_rules_proto//plugin/gogo/protobuf:protoc-gen-combo
@build_stack_rules_proto//plugin/gogo/protobuf:protoc-gen-gogo
@build_stack_rules_proto//plugin/gogo/protobuf:protoc-gen-gogofast
@build_stack_rules_proto//plugin/gogo/protobuf:protoc-gen-gogofaster
@build_stack_rules_proto//plugin/gogo/protobuf:protoc-gen-gogoslick
@build_stack_rules_proto//plugin/gogo/protobuf:protoc-gen-gogotypes
@build_stack_rules_proto//plugin/gogo/protobuf:protoc-gen-gostring
@build_stack_rules_proto//plugin/golang/protobuf:protoc-gen-go
@build_stack_rules_proto//plugin/grpc/grpc:protoc-gen-grpc-cpp
@build_stack_rules_proto//plugin/grpc/grpc:protoc-gen-grpc-python
@build_stack_rules_proto//plugin/grpc/grpc-go:protoc-gen-go-grpc
@build_stack_rules_proto//plugin/grpc/grpc-java:protoc-gen-grpc-java
@build_stack_rules_proto//plugin/grpc/grpc-node:protoc-gen-grpc-node
@build_stack_rules_proto//plugin/grpc/grpc-web:protoc-gen-grpc-web
@build_stack_rules_proto//plugin/scalapb/scalapb:protoc-gen-scala
@build_stack_rules_proto//plugin/scalapb/scalapb:protoc-gen-scala-grpc
@build_stack_rules_proto//plugin/scalapb/zio-grpc:protoc-gen-zio-grpc
@build_stack_rules_proto//plugin/stackb/grpc_js:protoc-gen-grpc-js
@build_stack_rules_proto//plugin/stephenh/ts-proto:protoc-gen-ts-proto