Introduces ResourceLoaderContext::getUserObj(), which gets
a (possibly cached) User object for the context's username.
Use this instead of the $wgUser global.
Change-Id: Ifd9f634db145381625ab68067ae67791a3f494b8
To do so, created ResourceLoader::createLoaderURL(), which takes a
ResourceLoaderContext object. ResourceLoader::makeLoaderURL() was
deprecated.
While reviewing usage of the old function, many of the callers only
differed by one or two parameters from their respective
ResourceLoaderContext object. To simplify that use case, I created
DerivativeResourceLoaderContext, based of off DerivativeContext for
IContextSource.
Change-Id: I961c641ab953153057be3e3b8cf6c07435e9a0b0
