Put status bar in immersive mode when in flex landscape split

* Split requests status bar to enter immersive mode when
device is
  * in split
  * landscape
  * 10:90 or 90:10 split
* One KI here is that when folding from home screen
the mIsLeftRightSplit value in SplitLayout doesn't get
computed correctly.

Bug: 383626044
Flag: com.android.wm.shell.enable_flexible_two_app_split
Test: Manual + unit tests
Change-Id: I8dd34e10251cc50e5b5fffae4e3018ce02e814ba