sparse: move function for resolving sparse matcher into core As part of the move, the function arguments changed so revs are passed as a list instead of *args. This allows us to use keyword arguments properly. Since the plan is to integrate sparse into core and have it enabled by default, we need to prepare for a sparse matcher to always be obtained and operated on. As part of the move, we inserted code that returns an always matcher if sparse isn't enabled. Some callers in the sparse extension take this into account and conditionally perform matching depending on whether the special always matcher is seen. I /think/ this may have sped up some operations where the extension is installed but no sparse config is activated. One thing I'm ensure of in this code is whether os.path.dirname() is semantically correct. os.posixpath.dirname() (which is exported as pathutil.dirname) might be a better choise because all patterns should be using posix directory separators (/) instead of Windows (\). There's an inline comment that implies Windows was tested. So hopefully it won't be a problem. We can improve this in a follow-up. I've added a TODO to track it.