Add wxBitmap::NewFromPNGData() for creating bitmaps from PNG data.

This simple function can be used to create a wxBitmap from the raw image data
in PNG format. It is just a thin wrapper around wxImage load functions under
almost all platforms but has two advantages:

1. It can be implemented natively for some platforms (currently only OS X).
2. It can be used in a single expression as it doesn't require creating a
   temporary wxMemoryInputStream and this will be required by wxBITMAP_PNG()
   macro that will be added soon.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72476 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/bitmap.h

@@ -83,6 +83,23 @@ protected:
 #define wxBITMAP_SCREEN_DEPTH       (-1)
 
 
+// ----------------------------------------------------------------------------
+// wxBitmapHelpers: container for various bitmap methods common to all ports.
+// ----------------------------------------------------------------------------
+
+// Unfortunately, currently wxBitmap does not inherit from wxBitmapBase on all
+// platforms and this is not easy to fix. So we extract at least some common
+// methods into this class from which both wxBitmapBase (and hase wxBitmap on
+// all platforms where it does inherit from it) and wxBitmap in wxMSW and other
+// exceptional ports (only wxPM and old wxCocoa) inherit.
+class WXDLLIMPEXP_CORE wxBitmapHelpers
+{
+public:
+    // Create a new wxBitmap from the PNG data in the given buffer.
+    static wxBitmap NewFromPNGData(const void* data, size_t size);
+};
+
+
 // All ports except wxMSW and wxOS2 use wxBitmapHandler and wxBitmapBase as
 // base class for wxBitmapHandler; wxMSW and wxOS2 use wxGDIImageHandler as
 // base class since it allows some code reuse there.
@@ -132,12 +149,12 @@ private:
     DECLARE_ABSTRACT_CLASS(wxBitmapHandler)
 };
 
-
 // ----------------------------------------------------------------------------
 // wxBitmap: class which represents platform-dependent bitmap (unlike wxImage)
 // ----------------------------------------------------------------------------
 
-class WXDLLIMPEXP_CORE wxBitmapBase : public wxGDIObject
+class WXDLLIMPEXP_CORE wxBitmapBase : public wxGDIObject,
+                                      public wxBitmapHelpers
 {
 public:
     /*