Proposal: Support for Embedding in Mock

Nobody has claimed this yet.

Certain interfaces may have a mechanism to guarantee that a specific type is embedded.

For example, the `Server` interface generated by `protoc-gen-go-grpc` contains an unexported `mustEmbedUnimplementedServer` method, which can be implemented by embedding the `UnimplementedServer` from the same package.

You can find more information here:
https://github.com/grpc/grpc-go/tree/master/cmd/protoc-gen-go-grpc#future-proofing-services

Real examples can be seen in the [helloworld example](https://pkg.go.dev/google.golang.org/grpc/examples/helloworld/helloworld) of grpc-go:

- https://github.com/grpc/grpc-go/blob/941102b7811f/examples/helloworld/helloworld/helloworld_grpc.pb.go#L72-L76
- https://github.com/grpc/grpc-go/blob/941102b7811f/examples/helloworld/helloworld/helloworld_grpc.pb.go#L83-L88

To support this pattern, I propose a feature that allows specified types to be embedded in mocks. For instance, how about running `moq -out mocks_test.go . MyInterface{Type1,Type2}` (or `MyInterface:MyMock{Type1,Type2}`) to embed Type1 and Type2 in MyInterface mock?

Start with the proposed embedding syntax and the protoc-gen-go-grpc future-proofing documentation, then inspect the linked helloworld_grpc.pb.go examples. The issue does not name moq files, tests, or an entry point, so the implementation scope and completion criteria need to be established before work begins.

Written by the indexing model from the issue text.