add raw-string literal support (#9956)

# Description

This PR adds raw string support by using `r#` at the beginning of single
quoted strings and `#` at the end.

Notice that escapes do not process, even within single quotes,
parentheses don't mean anything, $variables don't mean anything. It's
just a string.
```nushell
❯ echo r#'one\ntwo (blah) ($var)'#
one\ntwo (blah) ($var)
```
Notice how they work without `echo` or `print` and how they work without
carriage returns.
```nushell
❯ r#'adsfa'#
adsfa
❯ r##"asdfa'@qpejq'##
asdfa'@qpejq
❯ r#'asdfasdfasf
∙ foqwejfqo@'23rfjqf'#
```
They also have a special configurable color in the repl. (use single
quotes though)

![image](https://github.com/nushell/nushell/assets/343840/8780e21d-de4c-45b3-9880-2425f5fe10ef)

They should work like rust raw literals and allow `r##`, `r###`,
`r####`, etc, to help with having one or many `#`'s in the middle of
your raw-string.

They should work with `let` as well.

```nushell
r#'some\nraw\nstring'# | str upcase
```

closes https://github.com/nushell/nushell/issues/5091
# User-Facing Changes
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---------

Co-authored-by: WindSoilder <WindSoilder@outlook.com>
Co-authored-by: Ian Manske <ian.manske@pm.me>

crates/nuon/src/from.rs

@@ -319,7 +319,7 @@ fn convert_to_value(
             msg: "signatures not supported in nuon".into(),
             span: expr.span,
         }),
-        Expr::String(s) => Ok(Value::string(s, span)),
+        Expr::String(s) | Expr::RawString(s) => Ok(Value::string(s, span)),
         Expr::StringInterpolation(..) => Err(ShellError::OutsideSpannedLabeledError {
             src: original_text.to_string(),
             error: "Error when loading".into(),