[Wi-Fi] Fix Wi-Fi picker context menu 'Connect' button

1. Display the Wi-Fi dialog with MODE_CONNECT.
2. Connect with the WifiConfiguration from
   WifiConfigController2#getConfig() if it's available.

Bug: 152826354
Test: make RunSettingsRoboTests ROBOTEST_FILTER=WifiSettings2
Change-Id: Ifbe2ac30b1c37c8eab3227ac0561fdd2de5cb706

src/com/android/settings/wifi/WifiDialog2.java

@@ -214,4 +214,8 @@ public class WifiDialog2 extends AlertDialog implements WifiConfigUiBase2,
     public void setCancelButton(CharSequence text) {
         setButton(BUTTON_NEGATIVE, text, this);
     }
+
+    public WifiEntry getWifiEntry() {
+        return mWifiEntry;
+    }
 }