fix: treat CTRL + J as Enter

[ErichDonGubler]

This resolves the issue I noted having in nushell/nushell#6427 (comment), where hitting Enter in MacOS and Linux outside the main Reedline::read_line call in raw mode results in a CTRL + J event that yields no actual input once read_line is called again.

I'm not positive that this doesn't introduce regressions with, e.g., pasted input. I'm not sure what the best way to test this would be.

I'm also not sure if it resolves that issue in its entirety, since the question of whether its scope should include \n is unresolved.

[sholderbach]

I don't think hardcoding the binding like this is the right move, even if I can see it being part of the default binding. If you use the kitty keyboard extensions it may be possible to bind the true Ctrl-j then you probably want the ability to rewire it.

[ErichDonGubler]

I use Wezterm, so maybe there's some configuration I need to investigate there. I'm not currently aware of a way to rebind keys like that in Wezterm, but admittedly I haven't looked.