Extract the drawing logic from StartingSurfaceDrawer.

Prepare for windowless starting surface. Attemp to decouple the drawing
methods from window related handling.
Move most of snapshot drawing method together to a utility class
SnapshotDrawerUtils, so SystemBarBackgroundPainter now can shared for
shell and core.

Bug: 131727607
Bug: 257857570
Test: atest SnapshotDrawerUtilsTest StartingSurfaceDrawerTests
Test: hot launch an app, and verify snapshot starting window show up
without issue.
Test: cold launch app, verify icon style splash screen can show.

Change-Id: I4d2c04e41d375cf6c8711a60977b8f24dddd41c0