Fix onIsStashedChanged() not called in 3 button mode

Calling this ensures we update touchableRegion accordingly.

Since this will also start the stashed handle region sampling,
which we don't need for 3 button mode, also adjust logic to
check that the StashedHandleView is actually visible.

Flag: None
Test: Lock screen, run `adb shell cmd uimode night yes`, unlock
Test: Lock screen, rotate, unlock
  In both cases, verify touchableRegion is accurate
Fixes: 315393203
Change-Id: I951af6b97cad0ee0f362dc22f3996cfd9286a21e

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

@@ -149,7 +149,7 @@ public class StashedHandleViewController implements TaskbarControllers.LoggableT
         });
         initRegionSampler();
         if (mActivity.isPhoneGestureNavMode()) {
-            onIsStashedChanged(true);
+            onIsStashedChanged();
         }
     }
 
@@ -232,10 +232,10 @@ public class StashedHandleViewController implements TaskbarControllers.LoggableT
     }
 
     /** Called when taskbar is stashed or unstashed. */
-    public void onIsStashedChanged(boolean isStashed) {
-        mIsStashed = isStashed;
+    public void onIsStashedChanged() {
+        mIsStashed = isStashedHandleVisible();
         updateRegionSamplingWindowVisibility();
-        if (isStashed) {
+        if (mIsStashed) {
             mStashedHandleView.updateSampledRegion(mStashedHandleBounds);
             mRegionSamplingHelper.start(mStashedHandleView.getSampledRegion());
         } else {