b/418209286 Add new test case for using META + = to exit immersive mode to desktop mode

Test: USE_RBE=false atest WMShellFlickerTestsDesktopMode:com.android.wm.shell.flicker.keyboardshortcuts.ExitImmersiveToDesktopWithKeyboardShortcutFlickerTest -c (http://ab/I10600010432438824)
Video: http://recall/-/bIeL67gZQWi2chUZahS4zk
Flag: EXEMPT add new test case
Bug: 418209286
Change-Id: Ie59d94885dd5f7841e734e8ef3d9431a285329b9