[Chromecast][BLE] Queue disconnect requests and add API DisconnectAll

Bug: internal b/128536732
Bug: internal b/128464672
Test: cast_bluetooth_unittests, manual
Change-Id: I0a9234076d15296fe35edd0976b303a04a79cd5e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1524762
Reviewed-by: Yuchen Liu <yucliu@chromium.org>
Commit-Queue: Tiansong Cui <tiansong@google.com>
Auto-Submit: Tiansong Cui <tiansong@google.com>
Cr-Commit-Position: refs/heads/master@{#641226}
4 files changed