OSX wxBitmapBundle::FromFiles implementation for macOS (#2561)

* adding macOS wxBitmapBundle::FromFiles implementation

* adding FromFiles overload, generic implementation

* Update interface/wx/bmpbndl.h

* Removing outdated comment

Co-authored-by: VZ <vz-github@zeitlins.org>

include/wx/bmpbndl.h

@@ -87,6 +87,11 @@ public:
     // form name_2x or name@2x (and also using other factors) will be used.
     static wxBitmapBundle FromResources(const wxString& name);
 
+    // Create from files: all existing versions of the bitmap of the
+    // form filename_2x or name@2x (and also using other factors) will be used.
+    static wxBitmapBundle FromFiles(const wxString& fullpathname);
+    static wxBitmapBundle FromFiles(const wxString& path, const wxString& filename, const wxString& extension = wxASCII_STR("png"));
+
     // Create from existing implementation
     static wxBitmapBundle FromImpl(wxBitmapBundleImpl* impl);