[Dual Shade] Refactor ShadeHeader and ShadeOverlay UI code.

This includes simplifying the dependencies and structure of some of the
composables and view-models. This primarily includes:

* Avoiding passing factories to composables, but simpler types.

* Deleting some redundant state.

* Consolidating a few view models and associated factories to avoid
  unnecessary duplicate instantiation.

* Avoid creating the QQS view model in Dual Shade code.

* Adds a few missing unit tests.

* Remove the reference to DualShade.isEnabled (the flag is deprecated).

BONUS: Fix bug where QS header would show on large screens; it should
only show on handheld.

Bug: 384766545
Test: Unit tests still pass.
Test: Added new unit tests.
Test: Manually verified shade layout on both narrow and large screens.
Flag: com.android.systemui.scene_container
Change-Id: Ia6bb2de5d5f3d134b66f0b9fe78807bb94e82615