Bare word improvements (#8066)

# Description

This does two fixes for bare words:

* It changes completions for paths to wrap a path with backticks if it
starts with a number. This helps bare words that start with numbers be
separate from unit values
* It allows bare words wrapped with backticks to be the name of a
command. Backtick values in command positions are no longer treated as
strings

# User-Facing Changes

_(List of all changes that impact the user experience here. This helps
us keep track of breaking changes.)_

# Tests + Formatting

Don't forget to add tests that cover your changes.

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

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

tests/overlays/mod.rs

@@ -494,7 +494,7 @@ fn remove_overlay_discard_alias() {
 fn remove_overlay_discard_env() {
     let inp = &[
         r#"overlay use samples/spam.nu"#,
-        r#"let-env BAGR = `bagr`"#,
+        r#"let-env BAGR = 'bagr'"#,
         r#"overlay hide spam"#,
         r#"$env.BAGR"#,
     ];
@@ -526,7 +526,7 @@ fn remove_overlay_keep_decl() {
 fn remove_overlay_keep_alias() {
     let inp = &[
         r#"overlay use samples/spam.nu"#,
-        r#"alias bagr = `bagr`"#,
+        r#"alias bagr = 'bagr'"#,
         r#"overlay hide --keep-custom spam"#,
         r#"bagr"#,
     ];
@@ -542,7 +542,7 @@ fn remove_overlay_keep_alias() {
 fn remove_overlay_dont_keep_env() {
     let inp = &[
         r#"overlay use samples/spam.nu"#,
-        r#"let-env BAGR = `bagr`"#,
+        r#"let-env BAGR = 'bagr'"#,
         r#"overlay hide --keep-custom spam"#,
         r#"$env.BAGR"#,
     ];
@@ -596,7 +596,7 @@ fn remove_overlay_dont_keep_overwritten_alias() {
 fn remove_overlay_dont_keep_overwritten_env() {
     let inp = &[
         r#"overlay use samples/spam.nu"#,
-        r#"let-env BAZ = `bagr`"#,
+        r#"let-env BAZ = 'bagr'"#,
         r#"overlay hide --keep-custom spam"#,
         r#"$env.BAZ"#,
     ];
@@ -630,7 +630,7 @@ fn remove_overlay_keep_decl_in_latest_overlay() {
 fn remove_overlay_keep_alias_in_latest_overlay() {
     let inp = &[
         r#"overlay use samples/spam.nu"#,
-        r#"alias bagr = `bagr`"#,
+        r#"alias bagr = 'bagr'"#,
         r#"module eggs { }"#,
         r#"overlay use eggs"#,
         r#"overlay hide --keep-custom spam"#,
@@ -648,7 +648,7 @@ fn remove_overlay_keep_alias_in_latest_overlay() {
 fn remove_overlay_dont_keep_env_in_latest_overlay() {
     let inp = &[
         r#"overlay use samples/spam.nu"#,
-        r#"let-env BAGR = `bagr`"#,
+        r#"let-env BAGR = 'bagr'"#,
         r#"module eggs { }"#,
         r#"overlay use eggs"#,
         r#"overlay hide --keep-custom spam"#,

tests/shell/pipeline/commands/internal.rs

@@ -1258,6 +1258,13 @@ mod parse {
 
         assert!(actual.err.contains("extra positional argument"),);
     }
+
+    #[test]
+    fn ensure_backticks_are_bareword_command() {
+        let actual = nu!(cwd: ".", "`8abc123`");
+
+        assert!(actual.err.contains("was not found"),);
+    }
 }
 
 mod tilde_expansion {