Replace IsProofCheckEnabled() with GetProofCheckOptions()

This is more consistent with EnableProofCheck() and allows to retrieve
the current state of grammar checking under macOS, which can be checked
by user and so can be useful to know.

include/wx/gtk/textctrl.h

@@ -100,7 +100,7 @@ public:
     // Use native spelling and grammar checking functions.
     virtual bool EnableProofCheck(const wxTextProofOptions& options
                                     = wxTextProofOptions::Default()) wxOVERRIDE;
-    virtual bool IsProofCheckEnabled() const wxOVERRIDE;
+    virtual wxTextProofOptions GetProofCheckOptions() const wxOVERRIDE;
 #endif // wxUSE_SPELLCHECK && __WXGTK3__
 
     // Implementation from now on