[Flexiglas] Split shade - data layer

Data layer changes to support the split shade.

Split shade is the single panel shade that's shown for large screens and
unfolded devices where quick settings is one the left and notifications
is on the right.

Bug: 328473018
Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT
Test: see next CLs
Change-Id: I71264bca1493f4e82c37d9a7fb03f1847843a828