Update AccessibilityWindowManagerWithAccessibilityWindowTest

With this change, the test now uses the new code path enabled by
FLAG_COMPUTE_WINDOW_CHANGES_ON_A11Y.

Notable changes:
- Now injects a list of AccessibilityWindow, instead of WindowInfo.
- WindowInfo.layer is populated in A11yWindowManager. Removing related
  code.
- visible region is also computed in A11yWindowManager. Updating how
  they're tested.

Bug: 322444245
Bug: 325341171
Test: AccessibilityWindowManagerWithAccessibilityWindowTest
Change-Id: I6b1dc0116353eafc6589452f27d9cdc37aa84285