Support protobuf 4.x

Today grpc-web supports "google-protobuf": "~3.21.4".

Please add support for google-protobuff: 4.x

While using grpc-web 2.0.2 we get into the following de-serialization issue:
dataRead error: Error when deserializing response data; error: TypeError: reader.readPackedBool is not a function, response: undefined

Start by locating the google-protobuf dependency and the deserialization entry point that calls reader.readPackedBool. Reproduce the reported failure with protobuf 4.x while using grpc-web 2.0.2, then verify that protobuf 3.x behavior remains supported and the response deserializes successfully without the TypeError.

Written by the indexing model from the issue text.