Populate display id in A11yWindowManager

When window is removed, there can be a race between a11y and wm,
and sometimes A11yManagerService#sendA11yEvent cannot get a correct
display id.

There's also a case where a11y events for windowless windows don't have
a display id.

This change fixes the issue by populating display id in
A11yWindowManager#DisplayWindowsObserver for windows change events.

Bug: 240888087
Test: AccessibilityWindowManagerTest
Test: CtsAccessibilityServiceTestCases

Change-Id: I441d98e4431913ae24ab354423828d2a031b27b4