[flexiglass] "Inverts" dependency on media-in-compose

In ag/34856376, we added a dependency from Flexiglass on media-in-compose.
Aside from breaking a lot of end-to-end tests, it also disabled Flexiglass on AL devices unexpectedly.

Instead of having SceneContainerFlag.isEnabled require mediaControlsInCompose() to return true, this CL creates a
new MediaControlsInComposeFlag flag wrapper object with an isEnabled that would evaluate to true if either
media_controls_in_compose is true and/or if SceneContainerFlag.isEnabled evaluates to true (same thing as what we did for KeyguardWmStateRefactor).

This CL also replaces all current usages of mediaControlsInCompose() with MediaControlsInComposeFlag.isEnabled.

Fix: 436333780
Test: ran sysui, played media, and saw the media UI on all surfaces:
lock screen, shade, QS, and dual shade overlays
Flag: com.android.systemui.scene_container

Change-Id: I93b9e17a69f1b4a6ea4c902e499c3e5815e57e5d