Add annotations for polyglot

[pmlopes]

There is interest of using this from a polyglot side https://gitter.im/es4x/Lobby?at=5e158929821b826f5a84b787 Adding some basic annotations would ease the usability for this case and perhaps we can investigate if we can also update the code generator to include them too...

[vietj]

it is not clear what is the use case, can you elaborate ?

[vietj]

I'm unsetting this from 4.0.0 as the feature is not clear and it does not seem yet to be a focus for 4.0.0

[pmlopes]

The gRPC api isn't polyglot. Adding the required annotations would help the use from other languages. As a future bonus if the generator would add the annotations to the generated code that would also work. However the generator generates classes not interfaces so this won't work until this limitation is worked.

Having the first would already simplify the use.

[vietj]

gRPC can be used now from Groovy or Kotlin (I guess Scala too).

If I understand correctly the plan is that the generator add @VertxGen and then we code generate a polyglot wrapper ?