hgweb: port most @webcommand to use modern response type This only focused on porting the return value. raw file requests are wonky because they go through a separate code path at the dispatch layer. Now that everyone is using the same API, we could clean this up. It's worth noting that wsgirequest.respond() allows sending the Content-Disposition header, but the only user of that feature was removed as part of this change (with the setting of the header now being performed inline). A few @webcommand are not as straightforward as the others and they have not been ported yet. Differential Revision: https://phab.mercurial-scm.org/D2787