…by level and type

Co-authored-by: Bruce Weirdan <weirdan@gmail.com>

I think it makes more sense to have the errors that almost always appear
(level 7 errors) next to the errors that always appear, instead of
the level 1, least likely to appear errors being next to the ones that
always appear.

This also makes the order more similar to that output by the new
--by-issue-level format report.

Some time it might be nice to see if there's a way to auto generate most
of this docs page from the actual issue class definitions, or have
a test that checks the list of issues for each level is accurate and
complete.

…vel & type equal

PHP sorting only became stable in 8.0. For previous versions we would
still like duplicate issues to be sorted into a logical order.