help: remove now-redundant pointer to revsets help "hg help revisions" and "hg help revsets" now point to the same text, so drop the revsets reference.

help: eliminate duplicate text for revset string patterns There's no reason to duplicate this so many times, and it's likely an instance will be missed if support for a new pattern is added and documented. The stringmatcher is mostly used by revsets, though it is also used for the 'tag' related templates, and namespace filtering in the journal extension. So maybe there's a better place to document it. `hg help patterns` seems inappropriate, because that is all file pattern matching. While here, indicate how to perform case insensitive regex searches.

revset: add regular expression support to 'desc' This is a case insensitive predicate like 'author', so it conforms to the existing behavior of performing a case insensitive regex.

revset: stop lowercasing the regex pattern for 'author' It was probably unintentional for regex, as the meaning of some sequences like \S and \s is actually inverted by changing the case. For backward compatibility however, the matching is forced to case insensitive.