Enabled x button for clearable silent Notif[s]

Fixes: 204127880
Bug: 199902183
Test: RankingCoordinatorTest ShadeListBuilderTest
Merged-In: If55b0b7fc35bb6ece83878cf3db0d7abfc2a214a
Change-Id: If55b0b7fc35bb6ece83878cf3db0d7abfc2a214a
10 files changed