Create protoc-gen-cppstream tool to auto-generate cpp proto field Ids.

It is very similiar to protoc-gen-javastream, which generates field Ids used
by ProtoOutputStream.cpp to dump protobuf data.

Bug: 65641021
Test: compile the streaming_proto:
      $ mmm -j frameworks/base/tools/streaming_proto/
      and run:
      $ PATH=$PATH:out/host/linux-x86/bin/protoc-gen-cppstream aprotoc
      --cppstream_out=tmp/
      frameworks/base/core/proto/android/service/procstats.proto
      frameworks/base/core/proto/android/util/common.proto

Change-Id: I68becc80b5166455455c5df28cd698601b4a1c1d