Fix snapshots for secure windows

First, also draw system bar backgrounds when drawing a fake
snapshot. For that, refactor the drawing into a separate class so
it can be reused. Also enable fake snapshots for secure windows.

Test: com.android.server.wm.TaskSnapshotControllerTest
Test: com.android.server.wm.TaskSnapshotSurfaceTest
Test: Secure activity with resuming delay, make sure system bars
are covered when reopening app.

Bug: 35710126
Change-Id: I2f0ebc7e7acb80015780a4e882f0a472599efa30
diff --git a/services/core/java/com/android/server/wm/AppWindowContainerController.java b/services/core/java/com/android/server/wm/AppWindowContainerController.java
index c625cbe..b5e194b 100644
--- a/services/core/java/com/android/server/wm/AppWindowContainerController.java
+++ b/services/core/java/com/android/server/wm/AppWindowContainerController.java
@@ -36,7 +36,6 @@
 import android.os.Debug;
 import android.os.Handler;
 import android.os.IBinder;
-import android.os.Looper;
 import android.os.Trace;
 import android.util.Slog;
 import android.view.IApplicationToken;
@@ -319,7 +318,7 @@
                         + " token: " + mToken);
                 return;
             }
-            mContainer.setDisablePreviewSnapshots(disable);
+            mContainer.setDisablePreviewScreenshots(disable);
         }
     }