Properties missing for types that use `utils.Overwrite`

[clstokes]

Problem description

Documentation is missing for properties on interfaces/types that are extended using utils.Overwrite.

As one example, CallbackFunctionArgs extends BaseCallbackFunctionArgs and our docs show all the expected properties from these two types.

But, BaseCallbackFunctionArgs uses utils.Overwrite to overwrite FunctionArgs which contains description, environment, etc. that our docs do not include.

CallbackFunctionArgs   BaseCallbackFunctionArgs   FunctionArgs via utils.Overwrite

callback               code                       deadLetterConfig
callbackFactory        handler                    description
                       role                       environment
                       policies                   code
                       runtime                    name
                       codePathOptions            ...

                                                  ^ These are missing from API docs.

[iwahbe]

Our documentation is schema based, and we don't have schema support for language specific fields. Given that we want to move away from overlays, I don't think we want to add such support. Rather the solution is to move overlays into language specific libraries separate from the pulumi provider.