Improve CellPath display output (#14197)

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# Description
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Fixes: #13362

This PR fixes the `Display` impl for `CellPath`, as laid out in #13362
and #14090:

```nushell
> $.0."0"
$.0."0"

> $."foo.bar".baz
$."foo.bar".baz
```

# User-Facing Changes
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helps us keep track of breaking changes. -->

Cell-paths are now printed using the same `$.` notation that is used to
create them, and ambiguous column names are properly quoted.

# Tests + Formatting
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crates/nu-color-config/src/style_computer.rs

@@ -223,7 +223,7 @@ fn test_computable_style_closure_basic() {
         ];
         let actual_repl = nu!(cwd: dirs.test(), nu_repl_code(&inp));
         assert_eq!(actual_repl.err, "");
-        assert_eq!(actual_repl.out, "[bell.obj, book.obj, candle.obj]");
+        assert_eq!(actual_repl.out, r#"["bell.obj", "book.obj", "candle.obj"]"#);
     });
 }