Add an explicit media indicator icon to SysUI media controls

Checks for the value given by the key for explicit in MediaContants. And
applies all implementation necessary to show the explicit indicator as
an icon next to the artist name.

Bug: 221291466
Test: Manual - Checked apps that add explicit indicator to media.
Test: Checked with the media tester app.
Test: atest MediaDataManagerTest
Test: atest MediaControlPanelTest
Change-Id: I0721f098760e717b9ae32a8791fe68d5bac6e65f