Use wxCONTROL_FOCUSED control state flag when drawing native wxPG check box in the "modified state" under wxOSX.

Generally, wxCONTROL_PRESSED control flag is used when drawing native check box (wxPGEditor_CheckBox) in "modified state" but under wxOSX this flag is equivalent to wxCONTROL_CHECKED flag and hence it is necessary to indicate this state in an alternative way.

Closes #16696

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78212 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775