Use IRichEditOleCallback for wxTextCtrl's context menu.

In wxMSW, use IRichEditOleCallback::GetContextMenu() to provide our
default context menu for rich text controls, instead of using
EVT_CONTEXT_MENU.

The latter completely overrides native control's handling and in
particular breaks Windows 8's builtin spellchecking support.

Fall back to the previous non-OLE code for older richtext versions.

Also make the new MSWCreateContextMenu() method virtual so that the
context menu can be customized.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76723 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/textctrl.h

@@ -170,6 +170,11 @@ public:
     // EDIT control has one already)
     void OnContextMenu(wxContextMenuEvent& event);
 
+    // Create context menu for RICHEDIT controls. This may be called once during
+    // the control's lifetime or every time the menu is shown, depending on
+    // implementation.
+    virtual wxMenu *MSWCreateContextMenu();
+
     // be sure the caret remains invisible if the user
     // called HideNativeCaret() before
     void OnSetFocus(wxFocusEvent& event);