Add wxDisplay(wxWindow*) ctor with fall back on primary display

This is more convenient than calling GetFromWindow() and then checking
its return value.

interface/wx/display.h

@@ -26,6 +26,23 @@ public:
     */
     wxDisplay(unsigned int index = 0);
 
+    /**
+        Constructor creating the display object associated with the given
+        window.
+
+        This is the most convenient way of finding the display on which the
+        given window is shown while falling back to the default display if it
+        is not shown at all or positioned outside of any display.
+
+        @param window
+            A valid, i.e. non-null, window.
+
+        @see GetFromWindow()
+
+        @since 3.1.2
+     */
+    explicit wxDisplay(const wxWindow* window);
+
     /**
         Destructor.
     */