Support public imports

[ydnar]

A proto file imported from another proto file using import public ... will have its exported types aliased in the generated Go code, and vars copied. Currently the Go code generator doesn’t check to see if the imported symbols clobber existing symbols in the importing package.

• Ensure symbols imported using import public are renamed when aliased or copied into the destination package.
• Consider an option to rename the symbol in an importing package.

[flymedllva]

And is there an example of how to use with a buf?

[ydnar]

Great question. I’d accept an example with tests in a pull request.