Refactor owner drawn buttons drawing code in wxMSW.

Move it from wxCheckBox to wxControl to allow reusing this code in other
classes, notably wxRadioButton in the upcoming commits.

See #10137.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76455 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/checkbox.h

@@ -62,6 +62,8 @@ protected:
 
     virtual void DoSet3StateValue(wxCheckBoxState value);
     virtual wxCheckBoxState DoGet3StateValue() const;
+    virtual void MSWDrawButtonBitmap(wxWindow *win, wxDC& dc,
+                                     const wxRect& rect, int flags);
 
     // return true if this checkbox is owner drawn
     bool IsOwnerDrawn() const;