Fix [RTL] Wifi QR Scanner option overlaps wifi Password text

Use android:layout_alignParentStart & android:layout_alignParentEnd
to fix the RTL issue. And refine code of the scanner button.

Bug: 123923904
Test: manual test
Change-Id: I85491b99d22ec303e370422a81a43fc203b695fa

src/com/android/settings/wifi/WifiDialog.java

@@ -82,7 +82,6 @@ public class WifiDialog extends AlertDialog implements WifiConfigUiBase,
         mView = getLayoutInflater().inflate(R.layout.wifi_dialog, /* root */ null);
         final ImageButton scannerButton = mView.findViewById(R.id.password_scanner_button);
         if (scannerButton != null) {
-            scannerButton.setVisibility(View.VISIBLE);
             scannerButton.setOnClickListener((View v) -> {
                 String ssid = null;
                 if (mAccessPoint != null) {