Match name nesting and imports in .d.ts with .js files

[shaxbee]

Exported names were incorrectly mangled and didn't reflect types in * pb.js files, resulting in runtime errors where trying to instantiate.
Type aliases were replaced with proper nesting based on improbable-eng/ts-protoc-gen.
Aliased imports reflecting *pb.js files were added.
Services now return correct message types for external protos.

[stanley-cheung]

@shaxbee Thanks for this contributions. Can you give us an example on what this achieves? Like maybe a couple of simple .protos and what the current and new behavior would be? Thanks

[shaxbee]

@stanley-cheung Example generated code can be seen in shaxbee/grpc-web-dts-example

Code generated using master branch:

• Exported subclass names and messages from other packages are not present in master/example_pb.js.
• Nested type aliases result in compilation errors.

Code generated using typings-nesting-and-imports branch:

• Working imports from external protos
• Correct nesting
• Names matching generated js code

My intent with this and future typings pull requests is to provide feature parity with ts-protoc-gen and eventually prepare pull request to protobuf, so typings for messages are generated in protoc-gen-js plugin :-)

[stanley-cheung]

Thanks for the contributions!

[shinofara]

@stanley-cheung
I am waiting for the release.