IDEA-304758 - Add support for Nushell when loading environment

[shyim]

This fixes https://youtrack.jetbrains.com/issue/IDEA-304758, by adjusting the script when the shell is Nushell to | save <path>. Also escaped paths requires a ^ in nushell, otherwise it just outputs the path as a string.

I tested the change with Nushell and Bash. For every other shell, the generated script is exactly the same as before.

[ultinous-kszegi]

Any reason it can't be merged?