[Service] Add DDS stream manager

Add DdsStreamManager to manage stream subscriptions, event forwarding,
and event history buffers for the Dart Development Service.

TEST=pkg/dart_runtime_service_dds/test/dds_stream_manager_test.dart

Change-Id: I2f4afbbbb55b6005323e84b927b070df31c578bb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/541420
Commit-Queue: Ben Konyi <bkonyi@google.com>
Reviewed-by: Nicholas Shahan <nshahan@google.com>