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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# Tests + Formatting
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---------

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

src/ide.rs

@@ -569,6 +569,16 @@ pub fn hover(engine_state: &mut EngineState, file_path: &str, location: &Value)
                     }
                 })
             ),
+            FlatShape::RawString => println!(
+                "{}",
+                json!({
+                    "hover": "raw-string",
+                    "span": {
+                        "start": span.start - offset,
+                        "end": span.end - offset
+                    }
+                })
+            ),
             FlatShape::StringInterpolation => println!(
                 "{}",
                 json!({

src/tests/test_strings.rs

@@ -71,3 +71,23 @@ fn case_insensitive_sort_columns() -> TestResult {
         r#"[{"version":"four","package":"abc"},{"version":"three","package":"abc"},{"version":"two","package":"Abc"}]"#,
     )
 }
+
+#[test]
+fn raw_string() -> TestResult {
+    run_test(r#"r#'abcde""fghi"''''jkl'#"#, r#"abcde""fghi"''''jkl"#)?;
+    run_test(r#"r##'abcde""fghi"''''#jkl'##"#, r#"abcde""fghi"''''#jkl"#)?;
+    run_test(
+        r#"r###'abcde""fghi"'''##'#jkl'###"#,
+        r#"abcde""fghi"'''##'#jkl"#,
+    )?;
+    run_test("r#''#", "")?;
+    run_test(
+        r#"r#'a string with sharp inside # and ends with #'#"#,
+        "a string with sharp inside # and ends with #",
+    )
+}
+
+#[test]
+fn incomplete_raw_string() -> TestResult {
+    fail_test("r#abc", "expected '")
+}