wraps up SE-0004 and SE-0029.
I consider the diagnostic changes in Constraints/lvalues.swift to be
indicative of a QoI regression, but I'll deal with that separately.
Since the commit to deprecate “++” went through soon after the one to
deprecate C-style for loops, it’d be nice to auto-fix the for loops
even after previously changing ++ to += 1. So let’s do that.
Checked what it would look like to verify fix-its in every case, and
currently the tests are missing expected fix-its in 435 diagnoses in 60
test files.
So as an alternative, added support for a no fix-its marker “{{none}}”, and
added that marker to the c-style for deprecation tests where it applies.
Warns of deprecation, checks all the appropriate bits to see if we can
do an automatic fix, and generates fix-its if that is valid.
Also adds a note if the loop looks like it ought to be a simple
for-each, but really isn’t because the loop var is modified inside the
loop.
