backport #234 and #327 (and infra changes) to 1.1.x branch

[SethTisue]

specifically:

• fixes Parser returns an inappropriate failure msg when using repsep #233 on 1.1.x

but also more broadly:

• backports build/release infra to 1.1.x so we could actually perhaps release a 1.1.3

not clear yet if this will be for merge — I'm exploring the difficulty level

many of the changes I'm backporting here are of course not strictly necessary to backport, but they aren't harmful to backport either; the idea is to remove as many deltas between main and 1.1.x as reasonably possible, so that moving work back and forth between the branches will become easier again

Motivation

this is work for a client who wants to upgrade to 1.1.2 because it's the oldest version available for Scala 2.13; except that 1.1.2 includes #108 but doesn't include the followup PRs #234 and #327 which fixed #108's regressions, and those regressions are showing up in the client's own test suite

whereas by the time #234 and #237 landed, things had moved on and various 2.x changes were landing, including the removal of scala.util.parsing.json, which is still used here and there in minor ways by the client, so leaping all the way to some 2.x release would involve some cost/risk; stepwise upgrades are preferable when feasible

another possibility might be back to back-publish 1.1.1 for Scala 2.13, that wouldn't include #108 at all

[SethTisue]

I'm going to merge this — the 1.1.x branch is otherwise moribund, anyway, and there's nothing actually new here, it's all just backporting.

Then I'll see if I can roll a 1.1.3-RC1 using the backported publishing infra.

We can evaluate later whether we want to go to 1.1.3 final. In the meantime, if anyone wants to do some post-merge review on this, that would be entirely welcome!

[SethTisue]

see #460 for further work in this direction