typing: add type hints to mercurial/help.py
Was hoping to find more issues like f09bc2ed9100, but it may be that nothing
checks the args to that operation. In any event, the work is done and pytype
doesn't do a very good job inferring the types. A few of th emore complicated
things like the command table are left untyped, because they come from modules
that aren't typed yet.
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.