Support A11y overlay on multi-display

To make an a11y overlay window available on a specific display, we need
to update window token and update the context with a specific display
information when AccessibilityServiceConnection or diplay is changed.

Bug: 133304985
Test: a11y CTS & unit tests
Change-Id: Ib8693978e2455b5f568e195167e319b5b6cc9f02