Initial TaskbarUnitTestRule with example overlay controller tests.

Flag: TEST_ONLY
Bug: 230027385
Test: TaskbarOverlayControllerTest
Change-Id: I858906ece7e67677962ec8b4432bfcca5ec30283

quickstep/src/com/android/launcher3/taskbar/TaskbarManager.java

@@ -611,7 +611,8 @@ public class TaskbarManager {
         }
     }
 
-    private void addTaskbarRootViewToWindow() {
+    @VisibleForTesting
+    void addTaskbarRootViewToWindow() {
         if (enableTaskbarNoRecreate() && !mAddedWindow && mTaskbarActivityContext != null) {
             mWindowManager.addView(mTaskbarRootLayout,
                     mTaskbarActivityContext.getWindowLayoutParams());
@@ -619,7 +620,8 @@ public class TaskbarManager {
         }
     }
 
-    private void removeTaskbarRootViewFromWindow() {
+    @VisibleForTesting
+    void removeTaskbarRootViewFromWindow() {
         if (enableTaskbarNoRecreate() && mAddedWindow) {
             mWindowManager.removeViewImmediate(mTaskbarRootLayout);
             mAddedWindow = false;