feat: add new built-in condition for line ending

[weilbith]

Closes #592

[L3MON4D3]

Hey, nice 👍
TY!

[atticus-sullivan]

Working on #612, I've looked at this code again. Is there any reason why you're just comparing the amount of characters in the string? (comparing strings in lua should be as cheap as a pointer comparison afaik)

[L3MON4D3]

Mhmm, well number of characters works because both strings are the same line, so same lengths <=> same string.
I hadn't considered that just comparing them directly could be faster, but reading up on interning, that does seem to be the case (very interesting, I would've thought looking up the result after every string-operation leads to overall worse performance, but it seems to be more nuanced that that).
I'm definitely open to making this a direct comparison, best with a comment so it's clear that this might be/is faster than comparing lengths.

[atticus-sullivan]

Alright, then I guess I'll do this change in #612 (or new PR?)

[L3MON4D3]

Amend it, different commit, same PR is alright