Add permission for avoiding toast rate limiting.

I've decided to use a new permission since it needs to be added to
the settings app, which doesn't have INTERNAL_SYSTEM_WINDOW permission,
so I didn't want to add it as it may enable it to do some other things
it's not supposed to do.

Bug: 182448615
Test: atest android.widget.cts.ToastTest as regression test
Test: atest NotificationManagerServiceTest
Change-Id: I6adc84856f1fe9c33e0ad8470e7248a20587a1e9
diff --git a/packages/Shell/AndroidManifest.xml b/packages/Shell/AndroidManifest.xml
index b86ae6d..c7627f2 100644
--- a/packages/Shell/AndroidManifest.xml
+++ b/packages/Shell/AndroidManifest.xml
@@ -438,6 +438,9 @@
     <!-- Permission required for CTS test - ResourceObserverNativeTest -->
     <uses-permission android:name="android.permission.REGISTER_MEDIA_RESOURCE_OBSERVER" />
 
+    <!-- Permission required for CTS test - android.widget.cts.ToastTest -->
+    <uses-permission android:name="android.permission.UNLIMITED_TOASTS" />
+
     <application android:label="@string/app_label"
                 android:theme="@android:style/Theme.DeviceDefault.DayNight"
                 android:defaultToDeviceProtectedStorage="true"