resourceloader: Fix mw.loader to compute version for current request only

resourceloader: Fix mw.loader to compute version for current request only

Previously, the 'version' query parameter was computed before request-splitting
which meant that all requests within the same 'source/group'-batch carried the
same 'version' parameter. This was then consistently rejected on the server due
to it not batching the combined hash of modules for any given request.

In practice this happened very rarely (if at all) in production, because
urls don't usually hit anywhere near 2000 in common use.

Bug: T188076
Change-Id: I211523d4781623873887a05d048f56cccd28432c