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

src/osx/button_osx.cpp

@@ -101,6 +101,9 @@ void wxButton::SetLabel(const wxString& label)
     }
 
     wxAnyButton::SetLabel(label);
+#if wxOSX_USE_COCOA
+    OSXSetAcceleratorFromLabel(label);
+#endif
 }
 
 wxWindow *wxButton::SetDefault()