Re-add configure option for Direct2D QPA plugin

This also allows us to enable auto-detection for it.

Change-Id: I7639ab533553f02e691e6f6b8cdd8dff19d91809
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>

config_help.txt

@@ -252,6 +252,7 @@ Gui, printing, widget options:
   -xcb-xlib............. Enable Xcb-Xlib support [auto]
 
   Platform backends:
+    -direct2d .......... Enable Direct2D support [auto] (Windows only)
     -directfb .......... Enable DirectFB support [no] (Unix only)
     -eglfs ............. Enable EGLFS support [auto; no on Android and Windows]
     -gbm ............... Enable backends for GBM [auto] (Linux only)

src/gui/configure.json

@@ -9,6 +9,7 @@
         "options": {
             "android-style-assets": "boolean",
             "angle": "boolean",
+            "direct2d": "boolean",
             "directfb": "boolean",
             "directwrite": "boolean",
             "egl": "boolean",
@@ -446,8 +447,7 @@
         },
         "direct2d": {
             "label": "Direct 2D",
-            "autoDetect": false,
-            "condition": "config.win32 && libs.direct2d",
+            "condition": "config.win32 && !config.winrt && libs.direct2d",
             "output": [ "privateFeature" ]
         },
         "evdev": {