resourceloader: Restore "blocking" legacy modules

resourceloader: Restore "blocking" legacy modules

This ensures 'wikibits' and 'mediawiki.util' (if so configured)
finish loading before executing other modules.

This was previously implicitly provided for the bottom queue by
being in the top-queue, but since this is now asynchronous that
is no lower guaranteed. Fix this by making this explicit instead
of implicit.

Keep them in the top queue as-is to ensure consistency with cached
pages and it allows them to preload and batch in the same request
instead of being discovered later at run-time as a separate request.

Bug: T108124
Change-Id: I74e0cbe616404da927ea46d06308a7bae930eb69