[FR]: Support proto_library in other packages for ts_proto_library

[ryanli]

What is the current behavior?

Right now ts_proto_library only supports using depending on proto_library in the same package as it requires proto_srcs to be set, which takes file names as opposed to target names. This makes it impossible to include dependencies. See #627 for an example.

Describe the feature

ts_proto_library should be able to depend on protobuf messages and proto_library rules defined in other packages, and copy_files should copy them to the right place.