Only update handle alpha on system UI flag update.

Added logic to check if handle view alpha should be updated during SysUi
flag updates.

Fixes: 417125892
Test: Manual. Create a new bubble on the home screen, observe the stash
handle is not visible.
Have stashed bubble bar and multiple system languages.
Go to settings (or ane other apps that has input fields). Click on
search to trigger keyboard pop up. Observe that stash handle is hidden.
Collapse the keyboard and observe that stash handle is shown again.
Flag: EXEMPT bug-fix

Change-Id: I0976f37ca24ba816ee5eed6d4f1b4e6999b54c29

quickstep/src/com/android/launcher3/taskbar/bubbles/BubbleStashedHandleViewController.java

@@ -226,7 +226,6 @@ public class BubbleStashedHandleViewController {
     private void updateVisibilityForStateChange() {
         if (!mHiddenForSysui && !mHiddenForHomeButtonDisabled && !mHiddenForNoBubbles) {
             mStashedHandleView.setVisibility(VISIBLE);
-            mStashedHandleView.setAlpha(1);
         } else {
             mStashedHandleView.setVisibility(INVISIBLE);
             mStashedHandleView.setAlpha(0);