Fix Wi-Fi DPP fragment back stack problems

1. When a Wi-Fi network connected and receiving
   intent android.settings.PROCESS_WIFI_EASY_CONNECT_QR_CODE,
   show WifiDppAddDeviceFragment from WifiDppConfiguratorActivity
   instead of WifiNetworkListFragment

2. Only handle intent when savedInstanceState is null

3. To show a fragment
   I. do nothing when a fragment is already visible on screen,
   II. pop back stack if it's in back stack, we can do this because
   current fragment transactions are arranged in an order

Bug: 124194531
Test: atest WifiQrCodeTest
      atest WifiDppConfiguratorActivityTest
      atest WifiDppEnrolleeActivityTest
      atest WifiDppQrCodeGeneratorFragmentTest
      atest WifiDppQrCodeScannerFragmentTest
      atest WifiNetworkListFragmentTest
      atest WifiDppChooseSavedWifiNetworkFragmentTest

Change-Id: I1d44eeb3bdc7bfb2ec2e4d81efaab64b066651ad

tests/unit/src/com/android/settings/wifi/dpp/WifiNetworkListFragmentTest.java

@@ -98,7 +98,6 @@ public class WifiNetworkListFragmentTest {
     private void callOnWifiStateChanged(int state) {
         mActivityRule.getActivity().getMainThreadHandler()
                 .post(() -> mWifiNetworkListFragment.onWifiStateChanged(state));
-        mWifiNetworkListFragment.mUseConnectedAccessPointDirectly = false;
     }
 
     /** Launch the activity via an Intent with a String extra. */
@@ -173,4 +172,4 @@ public class WifiNetworkListFragmentTest {
         onView(withText(resourceString(WIFI_DISPLAY_STATUS_CONNECTED))).check(
                 matches(isDisplayed()));
     }
-}
+}