Fix activity leak

In some occasions, launcher leaks through DesktopVisibilityController
and SplitFromDesktopController. Set mDesktopVisibilityController and mSplitSelectStateController to null
after their onDestroy() methods are called.

Bug: 332339792
Test: m
Flag: ACONFIG com.android.window.flags.enable_desktop_windowing_mode TEAMFOOD
Change-Id: I66418f30ec5d2735f812ee6e4180f55f67d7b46f
1 file changed