Add bazel targets for standalone plugin binaries (#23919)

Follow-up to https://github.com/protocolbuffers/protobuf/pull/23736 and https://github.com/protocolbuffers/protobuf/pull/13308 but with only Bazel targets added per feedback.

This PR adds targets to build protoc plugins for all the built-in plugins. This will result in the following binaries being available:

- protoc-gen-cpp
- protoc-gen-csharp
- protoc-gen-java
- protoc-gen-kotlin
- protoc-gen-objectivec
- protoc-gen-php
- protoc-gen-python
- protoc-gen-pyi
- protoc-gen-ruby
- protoc-gen-rust

Closes #23919

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/23919 from bufdev:standalone-plugins 45d44f6e3a5cc318e4e06a0657399e202221c4ee
PiperOrigin-RevId: 917373434