b/399823963 Add new test case for using the app header menu to go from split...

b/399823963 Add new test case for using the app header menu to go from split screen to windowing mode

Test: USE_RBE=false atest
WMShellFlickerTestsDesktopMode:com.android.wm.shell.flicker.fundamentals.EnterDesktopFromSplitScreenWithAppHandleMenuFlickerTest
-c (http://ab/I80900010408882169)
Video: http://recall/-/fICpNRUDGx8z8yJ1DeClsL
Flag: EXEMPT add new test case
Bug: 399823963

Change-Id: Id76b73543c5d68aa5da74f4175edeaa40f737001