Make split screen have enter and exit animation

Remove MULTI_WINDOW mode block on loadAnimation to make transition
animation could show. And add some specific rule for split screen
because it should just like a full screen window but contain two
tasks.

Fix: 221117079
Test: manual
Test: pass existing tests
Change-Id: I6ccf0b5344d2bd11a2cd4eacba4df5cb9164e3e2