revlog: allow flag processors to be applied via store options
This allows flag processors to be registered to specific repos in an extension
by wrapping localrepo.resolverevlogstorevfsoptions(). I wanted to add the
processors via a function on localrepo, but some of the places where the
processors are globally registered don't have a repository available. This
makes targeting specific repos in the wrapper awkward, but still manageable.
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