[a11y] Set focus on "Pairing device" text once QR code is scanned.

Bug: 152462657

Test: Manual. Enable TalkBack in Settings > Accessibility. Navigate to
Developer options > Wireless debugging > Pairing device with QR code.
Scan a valid QR code, which should change to "Pairing device..." and
screen reader should say "Pairing device".

Change-Id: If467b56f787bda765fce1e5d46f8ab3c6210dc76

src/com/android/settings/wifi/dpp/AdbQrCode.java

@@ -15,6 +15,7 @@
  */
 package com.android.settings.wifi.dpp;
 
+import android.content.Context;
 import android.text.TextUtils;
 
 /**
@@ -53,4 +54,13 @@ public class AdbQrCode extends WifiQrCode {
     public WifiNetworkConfig getAdbNetworkConfig() {
         return mAdbConfig;
     }
+
+    /**
+     * Triggers a vibration to notify of a valid QR code.
+     *
+     * @param context The context to use
+     */
+    public static void triggerVibrationForQrCodeRecognition(Context context) {
+        WifiDppUtils.triggerVibrationForQrCodeRecognition(context);
+    }
 }