Cleaned up wxArtProvider:

1. Move platform-specific code for both GetSizeHint() and GetBitmap()
   into platform-specific files.
2. Introduced GetNativeSizeHint() to make native sizes better accessible,
   without having to understand weird GetSizeHint() semantics.
3. Fixed GetNativeSizeHint() to return sensible values in non-GTK ports;
   it returns wxDefaultSize if it can't make a good guess instead of
   returning arbitrary value.
4. Use 16x16 icons on MSW instead of 16x15: it works and is more
   'natural' size.



git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@56372 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -302,6 +302,9 @@ All:
 - Added wxString::Capitalize() and MakeCapitalized().
 - Added wxArray::swap().
 - Added wxSHUTDOWN_LOGOFF and wxSHUTDOWN_FORCE wxShutdown() flags (troelsk).
+- Added wxArtProvider::GetNativeSizeHint(); GetSizeHint() as well as
+  GetNativeSizeHint() now return more sensible values in wxMSW and wxMac and
+  no longer return bogus values.
 
 All (Unix):