Rewrite using protogen

[wdullaer]

This PR rewrites the plugin using the protogen framework rather than protoc-gen-star.

This brings a number of benefits:

• Removes the dependency on the deprecated github.com/golang/protobuf package
• Provides gomodule aware config options on how to generate code
• Consistent API with most modern go-protoc plugins
• Considerable reduction in LOC

Given that this is a very invasive change to the plugin, I completely understand if you do not want to merge. In this scenario, I will continue maintaining this under my own namespace as an alternative implementation.

The main driver for the change is the gomodule aware config options that using protogen brings.

[kei2100]

Thank you for your PR.

Your proposal makes sense and the code quality is excellent, so I'll incorporate the content of this PR.

However, I would like to use the same file names as before for the generated files, so I would like to make those changes and then create a new release over the weekend.

※ e.g. simple_marshall_zap.pb => simple.pb.marshall-zap.go

Many thanks!