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.