resourceloader: Use content-neutral context when computing module versions

resourceloader: Use content-neutral context when computing module versions

The startup module produces a manifest with versions representing the
entire module.

Typically, the request for the startup module itself has only=scripts.
However, that "only" must only apply to what resources of the startup module are
output in the request.

The context passed to getModifiedTime() and getVersionHash() must not suggest
any restriction of measuring only the scripts, or otherwise ignoring some
aspects of the module (such as stylesheets, or messages).

Most existing getModifiedTime() implementations compute timestamps of all
files, regardless of the context. So this bug didn't surface before.
However that will change for modules that compute the version hash based on
getModuleContent(), which does honour the getOnly() and shouldIncludeScripts()
methods of the request context.

Change-Id: Ib8f09c39d10724d146b53b6d53d82da18944a12b