normalize special characters in module names to allow variable access (#14353)

Fixes #14252

# User-Facing Changes

- Special characters in module names are replaced with underscores when
  importing constants, preventing "expected valid variable name":

```nushell
> module foo-bar { export const baz = 1 }
> use foo-bar
> $foo_bar.baz
```

- "expected valid variable name" errors now include a suggestion list:

```nushell
> module foo-bar { export const baz = 1 }
> use foo-bar
> $foo-bar
Error: nu::parser::parse_mismatch_with_did_you_mean

  × Parse mismatch during operation.
   ╭─[entry #1:1:1]
 1 │ $foo-bar;
   · ────┬───
   ·     ╰── expected valid variable name. Did you mean '$foo_bar'?
   ╰────
```

tests/repl/test_modules.rs

@@ -1,4 +1,5 @@
 use crate::repl::tests::{fail_test, run_test, TestResult};
+use rstest::rstest;
 
 #[test]
 fn module_def_imports_1() -> TestResult {
@@ -145,6 +146,28 @@ fn export_module_which_defined_const() -> TestResult {
     )
 }
 
+#[rstest]
+#[case("spam-mod")]
+#[case("spam/mod")]
+#[case("spam=mod")]
+fn export_module_with_normalized_var_name(#[case] name: &str) -> TestResult {
+    let def = format!(
+        "module {name} {{ export const b = 3; export module {name}2 {{ export const c = 4 }}  }}"
+    );
+    run_test(&format!("{def}; use {name}; $spam_mod.b"), "3")?;
+    run_test(&format!("{def}; use {name} *; $spam_mod2.c"), "4")
+}
+
+#[rstest]
+#[case("spam-mod")]
+#[case("spam/mod")]
+fn use_module_with_invalid_var_name(#[case] name: &str) -> TestResult {
+    fail_test(
+        &format!("module {name} {{ export const b = 3 }}; use {name}; ${name}"),
+        "expected valid variable name. Did you mean '$spam_mod'",
+    )
+}
+
 #[test]
 fn cannot_export_private_const() -> TestResult {
     fail_test(