Add wxLocale::GetOSInfo() and use it in MSW wxDateTimePickerCtrl.

This fixes the size of wxDateTimePickerCtrl in programs that don't set any
specific locale: previously, the standard "%m/%d/%y" format was used for
computing the best size of the control in this case, but this could have been
significantly shorter than the format actually used (compare with the default
"%d %b, %Y"), resulting in the control contents being truncated by default.

GetOSInfo() is currently different from GetInfo() only under MSW, but we might
need to make the same distinction under OS X too, so do make this function
public instead of keeping it MSW-specific.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78220 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/intl.h

@@ -421,6 +421,21 @@ public:
     static wxString GetInfo(wxLocaleInfo index,
                             wxLocaleCategory cat = wxLOCALE_CAT_DEFAULT);
 
+    /**
+        Get the values of a locale datum in the OS locale.
+
+        This function is similar to GetInfo() and, in fact, identical to it
+        under non-MSW systems. Under MSW it differs from it when no locale had
+        been explicitly set: GetInfo() returns the values corresponding to the
+        "C" locale used by the standard library functions, while this method
+        returns the values used by the OS which, in Windows case, correspond to
+        the user settings in the control panel.
+
+        @since 3.1.0
+     */
+    static wxString GetOSInfo(wxLocaleInfo index,
+                              wxLocaleCategory cat = wxLOCALE_CAT_DEFAULT);
+
     /**
         Initializes the wxLocale instance.