chore: refactor setting of auto-populated field in request

[parthea]

This PR depends on #16944. Please review #16944 first.

This PR addresses the feedback in #16944 (comment)

[gemini-code-assist]

Code Review

This pull request refactors the auto-population of UUID4 fields by centralizing the logic into a new _setup_request_id static method within the generated clients and updating shared macros to utilize it. Feedback indicates that the current implementation of _setup_request_id lacks proper support for dictionary and pure protobuf message types, which will lead to runtime errors. Additionally, the Jinja template condition for generating this method is incorrectly defined, causing it to be included as dead code even when no fields require auto-population.

[gemini-code-assist]

The implementation of _setup_request_id has two significant issues:

1. Correctness (Dict support): The docstring states that request can be a dict, but setattr and getattr will raise an AttributeError when called on a dictionary.
2. Correctness (Pure Protobuf support): For pure protobuf messages (non-proto-plus), the check field_name not in request will raise a TypeError because protobuf messages are not iterable.

To support both dictionary and message types (including pure protobuf and proto-plus), the logic should be more robust.

        if isinstance(request, dict):
            if is_proto3_optional:
                if field_name not in request:
                    request[field_name] = str(uuid.uuid4())
            elif not request.get(field_name):
                request[field_name] = str(uuid.uuid4())
            return

        if is_proto3_optional:
            try:
                # Pure protobuf messages
                if not request.HasField(field_name):
                    setattr(request, field_name, str(uuid.uuid4()))
            except (AttributeError, ValueError):
                # Proto-plus messages or other objects
                if field_name not in request:
                    setattr(request, field_name, str(uuid.uuid4()))
        else:
            if not getattr(request, field_name):
                setattr(request, field_name, str(uuid.uuid4()))

[gemini-code-assist]

The implementation of _setup_request_id does not correctly handle the dict type mentioned in the docstring (as setattr/getattr will fail), and it will raise a TypeError for pure protobuf messages when using the in operator on the message object. The logic should be updated to handle all supported request types.

        if isinstance(request, dict):
            if is_proto3_optional:
                if field_name not in request:
                    request[field_name] = str(uuid.uuid4())
            elif not request.get(field_name):
                request[field_name] = str(uuid.uuid4())
            return

        if is_proto3_optional:
            try:
                # Pure protobuf messages
                if not request.HasField(field_name):
                    setattr(request, field_name, str(uuid.uuid4()))
            except (AttributeError, ValueError):
                # Proto-plus messages or other objects
                if field_name not in request:
                    setattr(request, field_name, str(uuid.uuid4()))
        else:
            if not getattr(request, field_name):
                setattr(request, field_name, str(uuid.uuid4()))