upgrade repl to jline 3

[adriaanm]

I was sure I already had a ticket, but can't find it. We should do this by RC1. The other scheduled REPL improvements will have to wait until 2.13.x.

[som-snytt]

I'm looking into this today. It's non-trivial, but I'm more or less familiar with the previous state of affairs.

[fommil]

@hvesalai FYI ^^^

[hvesalai]

What what? Didn't I do this already? nope

I did this: scala/scala#6478

[fommil]

@hvesalai yeah, I thought you'd be the right guy for the job 😆

[som-snytt]

I worked on this, so I'll take a look. I haven't had time the past month...

[fommil]

sheesh @som-snytt , jline4 will be out by then... 😜

[som-snytt]

WIP scala/scala#7645

[adriaanm]

Excellent, thanks @som-snytt!

[som-snytt]

Supersession by scala/scala#8036

also I don't even care if they red squiggly my usage of supersession.

[SethTisue]

marked as blocker because we are willing to hold up 2.13.2 a bit if needed to make a serious attempt at this. (if we run into unexpectedly serious trouble, postponing remains possible.)