Add API to disable snapshotting of activities

Test: runtest frameworks-services -c
com.android.server.wm.TaskSnapshotControllerTest
Test: Launch DisableScreenshotsActivity, go to recents, make sure
content is white.
Bug: 31339431

Change-Id: I329925d2fca389e561da3389a67fe888b5bb1033
diff --git a/tests/ActivityTests/AndroidManifest.xml b/tests/ActivityTests/AndroidManifest.xml
index 7b9c9f1..4dd51dc 100644
--- a/tests/ActivityTests/AndroidManifest.xml
+++ b/tests/ActivityTests/AndroidManifest.xml
@@ -79,5 +79,12 @@
             android:singleUser="true" android:exported="true" />
         <receiver android:name="TrackTimeReceiver" />
         <receiver android:name="AlarmSpamReceiver" />
+        <activity android:name="DisableScreenshotsActivity"
+                android:label="DisableScreenshots">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
     </application>
 </manifest>