resourceloader: Implement ResourceLoaderRawFileModule for 'mediawiki.js'

resourceloader: Implement ResourceLoaderRawFileModule for 'mediawiki.js'

When adding files to this module, they all imply a global scope.
While most files have their own closure, it is still inconsistent
with normal modules which always have a closure via mw.loader.implement.

Base modules like 'mediawiki' are lacking such a closure, thus making
it hard to share variables within the different files that make up the
module without making it a globally public.

The use case is 13203c0a2180e5, where we could expose the sha1()
library within the scope of this module only.

Change-Id: I93fcd045f47ec6a595b26f739939e1d371832ac9