[flexiglass] LockscreenSceneLayout

A Compose slot-based smart layout for the lockscreen scene. It handles
the measurement and positioning of all of the elements on the lockscreen
scene based on the current form factor, folding posture, orientation,
etc.

Bug: 395060439
Bug: 405383415
Bug: 396218588
Bug: 396202921
Bug: 384077475
Bug: 394875986
Bug: 405366494
Bug: 390988286
Test: verified in testbed app and with followup CL(s) on this chain
Flag: com.android.systemui.scene_container
Change-Id: I2b7e0c1d2b5ddf4f335a990d13a72f88237292e0