Fix splitting with wrong apps when entering split with rotation

Use mSplitRequest to determine if it's entering split instead, rename
the flag to mIsDividerRemoteAnimating which is more accurate to what it
stands for. When reseting divider remote animating flag, it should not
affect other logic for entering split screen besides divider visibility.

Fix: 269712647
Test: atest WMShellUnitTests WMShellFlickerTests
Test: repro steps of the bug
Change-Id: Ic4ed1b9f96bd96c7f52a7f1d64ddbad0d4b76b12