JVM Plugin does not maintain generated stubs well

[matt2e]

Issues:

• After being told about other module schemas, the plugin generates schema protos for each module (excluding modules dependant on itself). It does not generate actual client code for them though, so the user can not easily import those files with autocomplete. The next build of the module will generate those files.
• If a module is removed, or it becomes dependant on the a module, that module's proto file will not get removed (writeGenericSchemaFiles adds but never removes)
• If we trigger a new build every time an external module schema changes then do things become cyclic? I guess not but still a lot of unnecessary builds... (10 module project... every schema change causes 10 builds)

Would switching to the same model we use for go where we generate external stubs once in projectroot/.ftl and then we could symlink into it from within each jvm target?

[matt2e]

Simply clearing out old proto files in writeGenericSchemaFiles makes things worse as the initial builds with ftl dev will not generate non-dependant external sources every time.

[matt2e]

Closing as I think this is a good solution for now: #4066