Add support for Ahead-of-Time QML cache generation when using the Qt resource system

QML cache files can only be used at the moment with code that expects the original QML documents to be placed in the file system. Many applications are using the Qt resource system to avoid the need to deploy QML documents in the file system.

It would be good to support the Qt resource system with cache files.

This could be achieved by using a resource based loading infrastructure like with the Qt Quick Compiler, and then deploy the cache files either in the file system or by making it possible for qmlcachegen to generate object files for Mach-O, ELF and COFF.