shell32: shell icon cache and icon extractors need to be rewritten

The code that loads icons is fully functioning however in order to fix all the issues with icons showing slow as hell we should consider rewriting the components that handle icons. For example we will benefit greatly in terms of user experience if we implement asynchronous icon extraction, accessing the icons in the SIC using a hash table, caching the icon cache in a file instead of rebuilding it in each boot, and implement any other features windows may have in these components. A rewrite will also use c++ classes instead of using the existing C interfaces. However these goals are not a priority and will only give a user experience improvement as the existing implementation is functioning. It's just sub optimal.