[bc25] Set overlay shade entry points from Lockscreen and Gone scenes.

This takes us one step closer to deprecating the obsolete shade scenes.

Bug: 338577208
Bug: 356596436
Flag: com.android.systemui.scene_container
Flag: com.android.systemui.dual_shade
Test: Manually verified by swiping down from the top left and right
 edges on both Lockscreen and Gone scenes and observing that the
 appropriate shade overlay opened.
Test: Added new unit tests.
Test: Existing unit tests still pass.
Change-Id: I47d3aaa76bce51f89dd2d7a4a50caa54331027ab