[mojo-bindings] Clean-up/augment new binding types

Adds minor API features and fixes some bugs in the Remote/Receiver types
to support further conversion of code away from InterfacePtr etc.

Bug: 875030
Change-Id: Ia001195c8fd0feed669d3cd65f501ace55de3015
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1574896
Reviewed-by: Oksana Zhuravlova <oksamyt@chromium.org>
Commit-Queue: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#652636}
7 files changed