Reduce switch split flicker on protrait split

Due to insets for tasks would be changed when switch split on
protrait mode, it lead to some flicker.
Attach screenshots before switch and fading out after switch
animation finished to reduce flicker.
Also update animation algorithm to reduce flicker occured when
top to bottom case.

Fix: 240517067
Test: manual
Test: pass existing tests
Change-Id: I66991b40b2ab8f410abcb800e9ca6e80222faa8c