widl: Remove duplicated code in the form of the write_struct_expr function by enhancing write_expr to allow toplevel identifiers to be prefixed by a string, if specified.

Remove the conversion of pointer types into base types as this was only 
needed due to lack of proper type resolving.

Also check that expressions return the correct type for the attribute.

widl: Pass the actual type into check_remoting_fields and check_field_common instead of the type name.

uxtheme: Speed up UXTHEME_SizedBlt in the ST_TILE by building an appropriately-sized memory bitmap out of the tile instead of iterating with UXTHEME_Blt() directly.