resourceloader: Don't cache stale responses in mw.loader.store

resourceloader: Don't cache stale responses in mw.loader.store

Follows-up 6fa1e56. This is already fixed for http caches by
shortening the Cache-Control max-age in case of a version mismatch.

However the client still cached it blindly in mw.loader.store.
Resolve this by communicating to the client what version of the module
was exported. The client can then compare this version to the version
it originally requested and decide not to cache it.

Adopt the module key format (name@version) from mw.loader.store
in mw.loader.implement() as well.

Bug: T117587
Change-Id: I1a7c44d0222893afefac20bef507bdd1a1a87ecd