Improve shell transition of dismiss by divider

This is to avoid jank or flicker when dismiss split by divider.

Bug: 258241450
Test: manual
Test: atest WMShellFlickerTests:DismissSplitScreenByDivider
Test: atest SplitTransitionTests
Change-Id: I9036c8cdf4a844f4b8572fe76df2dbc5aa8c4e49
3 files changed