Make only the "Add Network" WifiDialog fullscreen.

Fixes an issue where other instances of WifiDialog were being launched
fullscreen. Creates static methods for creating fullscreen and modal
WifiDialogs to make the style more explicit.

Bug: 63889135
Test: make -j40 RunSettingsRoboTests
Change-Id: I2200b5d7f817b9f69a6abb73bf2c04ea24556d19

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

@@ -55,7 +55,7 @@ public class WifiDialogActivity extends Activity implements WifiDialog.WifiDialo
             accessPoint = new AccessPoint(this, accessPointState);
         }
 
-        WifiDialog dialog = new WifiDialog(this, this, accessPoint, WifiConfigUiBase.MODE_CONNECT);
+        WifiDialog dialog = WifiDialog.createModal(this, this, accessPoint, WifiConfigUiBase.MODE_CONNECT);
         dialog.show();
         dialog.setOnDismissListener(this);
     }