Clean up a11y overlays after service exits or crashes.

Fix: 271490102
Test: atest AccessibilityOverlayTest
Change-Id: I1443d2c98c6ba4801a2e71b247fac7d662173bdf
diff --git a/services/accessibility/accessibility.aconfig b/services/accessibility/accessibility.aconfig
index 75ecdb7..a19920f 100644
--- a/services/accessibility/accessibility.aconfig
+++ b/services/accessibility/accessibility.aconfig
@@ -10,6 +10,13 @@
 }
 
 flag {
+    name: "cleanup_a11y_overlays"
+    namespace: "accessibility"
+    description: "Removes all attached accessibility overlays when a service is removed."
+    bug: "271490102"
+}
+
+flag {
     name: "deprecate_package_list_observer"
     namespace: "accessibility"
     description: "Stops using the deprecated PackageListObserver."