Improve error when regex rejects pattern. Resolution of #8037 (#8050)

# Description

Improve error when `str replace <pattern>` detects a problem with
<pattern>.

# User-Facing Changes

New "Incorrect value" error:
```
〉 'C:\Users\kubouch' | str replace 'C:\Users' 'foo'
Error: nu:🐚:incorrect_value (link)

  × Incorrect value.
   ╭─[entry #1:1:1]
 1 │  'C:\Users\kubouch' | str replace 'C:\Users' 'foo'
   ·                                   ─────┬────
   ·                                        ╰── Regex error: Parsing error at position 4: Invalid hex escape
   ╰────
```

We could fruitfully replace some of the current uses of
`ShellError::UnsupportedInput` with this error. 'Incorrect value' is
different from 'wrong type'

# Tests + Formatting

Don't forget to add tests that cover your changes.
* none added / changed.

Make sure you've run and fixed any issues with these commands:

- [x] `cargo fmt --all -- --check` to check standard code formatting
(`cargo fmt --all` applies these changes)
- [x] `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- [x] `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-command/tests/commands/str_/mod.rs

@@ -199,6 +199,26 @@ fn find_and_replaces_without_passing_field() {
     })
 }
 
+#[test]
+fn regex_error_in_pattern() {
+    Playground::setup("str_test_8", |dirs, _sandbox| {
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                 'source string'
+                 | str replace 'source \Ufoo' "destination"
+             "#
+        ));
+
+        let err = actual.err;
+        let expecting_str = "Incorrect value";
+        assert!(
+            err.contains(expecting_str),
+            "Error should contain '{expecting_str}', but was: {err}"
+        );
+    })
+}
+
 #[test]
 fn substrings_the_input() {
     Playground::setup("str_test_8", |dirs, sandbox| {