New hearing device pairing page: fix cannot re-connecting gatt issue

Should clear the `mConnectingGattList` when the gatts in the list are all disconnected in `OnStop()`. Otherwise, we can't re-connecting gatt for these devices after the page enter `onStart()` again.

Bug: 307890347
Test: manual test
Change-Id: I3b9fe05f894548887339011f5757c71e3a40eb5c

src/com/android/settings/accessibility/HearingDevicePairingFragment.java

@@ -149,6 +149,7 @@ public class HearingDevicePairingFragment extends RestrictedDashboardFragment im
         for (BluetoothGatt gatt: mConnectingGattList) {
             gatt.disconnect();
         }
+        mConnectingGattList.clear();
         mLocalManager.setForegroundActivity(null);
         mLocalManager.getEventManager().unregisterCallback(this);
     }