Ignore ACTION_DOWN events when mTracking is true

This is a partial fix for b/198553252 that lessens the effects and
prevents possible side effects but does not address the root cause,
which is the fact that these events are ACTION_DOWN instead of
ACTION_POINTER_DOWN. The second finger touches do cause the height
of the shade to jump, which is not ideal, but it was unanimously
preferred over dismissing the shade when I polled the team.

Test: manual and atest
Bug: 198553252
Change-Id: I8b087bd435622dcc66e98c731cee1558272be515

packages/SystemUI/src/com/android/systemui/shade/NotificationPanelViewController.java

@@ -6135,6 +6135,11 @@ public final class NotificationPanelViewController implements Dumpable {
 
             switch (event.getActionMasked()) {
                 case MotionEvent.ACTION_DOWN:
+                    if (mTracking) {
+                        // TODO(b/247126247) fix underlying issue. Should be ACTION_POINTER_DOWN.
+                        mShadeLog.d("Don't intercept down event while already tracking");
+                        return false;
+                    }
                     mCentralSurfaces.userActivity();
                     mAnimatingOnDown = mHeightAnimator != null && !mIsSpringBackAnimation;
                     mMinExpandHeight = 0.0f;
@@ -6222,6 +6227,11 @@ public final class NotificationPanelViewController implements Dumpable {
                             "onTouch: duplicate down event detected... ignoring");
                     return true;
                 }
+                if (mTracking) {
+                    // TODO(b/247126247) fix underlying issue. Should be ACTION_POINTER_DOWN.
+                    mShadeLog.d("Don't handle down event while already tracking");
+                    return true;
+                }
                 mLastTouchDownTime = event.getDownTime();
             }