Prevent dim update during onImePositionChanged for 10:90/90:10 split

This change disables the split screen dim update when the IME position changes and the split ratio is either 10:90 or 90:10. This resolves an issue where the screen would dim unnecessarily in these specific split configurations.

Bug: 412841648
Flag: com.android.wm.shell.enable_flexible_two_app_split
Test: EXEMPT bug fix, manual test
Change-Id: Ife3d72434c0ad7f1bc30c4e8238681116b470f8a