improve the readability of generated gRPC client files

[devoncarew]

Improve the readability of generated gRPC client files:

• emit the method descriptors at the end of the client class definition (after the service methods)
• emit the foo_Pre() and foo() methods together, instead of in separate parts of the service base class

[devoncarew]

It looks like pub publish --dry-run is having trouble w/ the goldens in test/ (which we don't expect to be analyzed):

Validating package...
  Package validation found the following potential issue:
  * line 16, column 1 of test/goldens/grpc_service.pbgrpc.dart: This package does not have grpc in the `dependencies` or `dev_dependencies` section of `pubspec.yaml`.
       ╷
    16 │ import 'package:grpc/service_api.dart' as $grpc;
       │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
       ╵

We may need to move them into a directory which pub publish doesn't try to analyze, ignore the goldens somehow from the POV of pub, or make the files analyze correctly.

[mosuem]

We may need to move them into a directory which pub publish doesn't try to analyze, ignore the goldens somehow from the POV of pub, or make the files analyze correctly.

I think I normally do a test_data folder outside of test to avoid these kinds of issues. Not sure if it helps here.

[devoncarew]

I think I normally do a test_data folder outside of test to avoid these kinds of issues. Not sure if it helps here.

I think in this case it will not; we're running into issues w/ the validations for 'pub publish' not being configurable. Using test_goldens may be more hygenic however; perhaps a future refactoring.