Fix IME Overlay Layering Target visibility updates

In [1] we started tracking the visibility of the IME Input Target, and
the IME Overlay Layering target (i.e. IME Layering Target that has
FLAG_NOT_FOCUSABLE and FLAG_ALT_FOCUSABLE_IM).

If there is a visible IME Overlay Layering Target, and the IME Input
Target becomes invisible, then we hide the IME. In this case, the IME
Input Target won't be updated, as the layering target is not focusable.
If we wouldn't explicitly hide, the IME would show on the new layering
target, using the requestedVisibleTypes of the (now outdated) input
target.

However, the initial issue tracked by [1] is still reproducible.
Moreover, this state update is quite brittle, and in many cases left
with an outdated value, which leads to InputMethodManagerService sending
explicit IME hide request, because at some point we had a visible IME
Overlay Layering target, and we didn't reset the state properly.

This will first make sure we update this state properly when needed,
with a follow up CL tracking this state removal, as well as a proper fix
to the initial issue (252192121).

  [1]: Ia71b975898efb19439c3a1b1a9a2bdcf21b78650

Flag: EXEMPT bugfix
Bug: 407125743
Test: atest DisplayContentTests#testDispatchImeOverlayLayeringTargetVisibilityChanged_whenLayeringTargetNull
  DisplayContentTests#testDispatchImeOverlayLayeringTargetVisibilityChanged_whenLayeringTargetChanges
  DisplayContentTests#testDispatchImeOverlayLayeringTargetVisibilityChanged_whenOverlayTargetAdded
Change-Id: I3ddcc49947f68a18216551bc9434ce453debdeea