Add google.protobuf.Any.unpack function

[fubhy]

Currently, in order to unpack into a message instance, you have to do:

  const any = ... // Some arbitrary `google.protobuf.Any` any.
  const message = registry.findMessage(typeName);
  const instance = new message!();
  any.unpackTo(instance);

It would be great if google.protobuf.Any was generated with a utility for that accepting a typeRegistry as input.

[smaye81]

Hey @fubhy. This was actually something on our roadmap also. Any interest in putting up a PR?

[fubhy]

Yep. Will do!

[fubhy]

#288