New Pipeline: Show media on lockscreen

* Renames MediaHeaderView to MediaContainerView for clarity.
* Adds a NodeController (MediaContainerController) which also handles reinflation.
* NodeSpecBuilder, which was already responsible for adding section headers, is now also responsible for adding MediaContainerView.

Fixes: 213174143
Test: atest NotificationSectionsManagerTest NodeSpecBuilderTest KeyguardMediaControllerTest
Change-Id: I56ff72f84b1206d4b7fd3a735fe567e72eac8f9e