Introduce ImeVisibilityStateComputer

With go/new-ime-visibility-control-u, this CL introduced following
classes to aim to improve our IME visiblity control protocal with
per-window state tracking:

- ImeVisibilityStateComputer:
  To compute the IME visibility state according the given WindowState
  from the focused window, or the app requested IME visibility
  from InputMethodManager.

- ImeVisibilityStateComputer.ImeTargetWindowState:
  Represents the current state of a window that focused by
  the Input Method

- ImeVisibilityStateComputer.ImeVisibilityPolicy:
  To manage all IME related visibility policies or configurations.

Note that the above classes is a preperation CL with only refactoring
& moving some checking IME visibility methods logic from IMMS side to
the computer, basically it should not have any behavior change.

Bug: 246309664
Test: atest CtsInputMethodTestCases
Change-Id: Id1115ceb951e4bb0361a32b824d966cc70b7d132