Do not keep focus on IME dialog if its target is invisible

Otherwise the input method target won't have a change to be
updated from IMMS for new focus window.

And if input method target doesn't update, the IME and IME
Switcher Menu will be invisible because they are put under
ImeContainer which is put on invisible app's surface.

Fix: 359711526
Flag: EXEMPT bugfix
Test: atest DisplayContentTests# \
      testImeMenuDialogFocusWhenImeLayeringTargetChanges

Change-Id: Ia5ea318b2a92ccc003f3192a198bf041365f70cf