REPL: newline auto-indents like line above

[rfourquet]

This is a dumb heuristic, but easily predictable, and probably more useful than the current behavior of placing the cursor at the beginning of the line.
To make it more practical, this is probably conditionned to merging #22939 first, because the pattern of needing to delete 1 indentation (i.e. 4 spaces at a time) would become much more common.

[rfourquet]

This would be ready to go now. One question is whether auto-indent is the default (my vote is yes).

[rfourquet]

Given the 3 upvotes, I will keep auto-indent as the default and will merge in a couple of days if no objecting comment.

[fredrikekre]

This is very nice! But would be very annoying without #22939 👍

[StefanKarpinski]

I think this messed up pasting repl code:

julia> for i = 1:10
           println(i)
           # didn't need to press tab here!
       end
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julia> for i = 1:10
                  println(i)
                  # didn't need to press tab here!
              end
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I typed the first one with the lovely new auto-indent, then cut the whole input and output and pasted it back into the REPL, which resulting in double indents in the pasted code.

[rfourquet]

Oups sorry! I will investigate ASAP.

[StefanKarpinski]

No worries – lots of moving parts in the REPL code!

[rfourquet]

Actually, I see the same behavior in the oldest julia I have from almost 2 months ago; can you confirm that you observe this problem only since this PR? (And I still can't think of a change made here that could break this pasting behavior; but surely needs to be investigated anyway!)

[KristofferC]

I have also seen this previously and can repo on an oldish master.

[Keno]

I've also seen this before (should still be fixed of course).

[fredrikekre]

Here is something that has to be caused by this:
https://asciinema.org/a/QMnau9w3uZzogut7QfhYct3YP?t=7