slimerjs: added xulrunner as resource

This is an alternative pull request for #22914 , which adds xulrunner as a resource to slimerjs formula.

The problem with slimerjs just depending on xulrunner as in #22914 is, that xulrunner is designed to generate a framework on os x, which can be used by 3rd party apps. We can't symlink the xulrunner executable into bin (which would be enough to be recognized by slimerjs), since xulrunner asumes, that all dylibs are in the same folder as the executable, which is not the case if you run it through the symlink (Couldn't load XPCOM error).

This PR will add xulrunner to the slimerjs files in the same way as in the slimerjs standalone edtion with the difference that we compile xulrunner from source instead of shipping precompiled binaries from mozilla.

We may also want to change this to ship with xulrunner as default and a option to build without xulrunner. (I don't know if this is necessary for creating a bottle for it or if we can create a bottle for a --with-xulrunner build only)