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.

crates/nu-cli/src/completions/file_completions.rs

@@ -141,6 +141,16 @@ pub fn file_path_completion(
                             || path.contains('#')
                             || path.contains('(')
                             || path.contains(')')
+                            || path.starts_with('0')
+                            || path.starts_with('1')
+                            || path.starts_with('2')
+                            || path.starts_with('3')
+                            || path.starts_with('4')
+                            || path.starts_with('5')
+                            || path.starts_with('6')
+                            || path.starts_with('7')
+                            || path.starts_with('8')
+                            || path.starts_with('9')
                         {
                             path = format!("`{path}`");
                         }