Basic accessibility support for picture-in-picture

Exposing actions from the PIP InputConsumer to accessibility,
stripping all actions from a covered PIP app, and adding the
InputConsumer's actions on the PIP app's root view.

We were also using an "undefined" accessibility ID to mean
three different things: a root view, a host view of a virtual
view hierarchy, and a truly undefined view. I've introduced
new values for cases where the id could be defined.

Also gathering all window IDs into one place to reduce the
chance of collisions.

Bug: 34773134
Test: In progress. Current cts passes.
Change-Id: I97269741a292cf406272bf02359c76c396f84640
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 5a5ed88..58e60e5 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -2305,6 +2305,10 @@
     <permission android:name="android.permission.RETRIEVE_WINDOW_TOKEN"
         android:protectionLevel="signature" />
 
+    <!-- @hide Allows an application to modify accessibility information from another app. -->
+    <permission android:name="android.permission.MODIFY_ACCESSIBILITY_DATA"
+                android:protectionLevel="signature" />
+
     <!-- @hide Allows an application to collect frame statistics -->
     <permission android:name="android.permission.FRAME_STATS"
          android:protectionLevel="signature" />