Implement support for button mnemonics in wxOSX/Cocoa.

Set the mnemonic as "key equivalent".

Closes #12917.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72809 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/osx/button.h

@@ -49,6 +49,10 @@ public:
 
     virtual bool        OSXHandleClicked( double timestampsec );
 
+#if wxOSX_USE_COCOA
+    void OSXSetAcceleratorFromLabel(const wxString& label);
+#endif
+
 protected:
     DECLARE_DYNAMIC_CLASS(wxButton)
 };