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-command/src/filters/flatten.rs

@@ -157,7 +157,7 @@ fn flat_value(columns: &[CellPath], item: Value, all: bool) -> Vec<Value> {
             let mut inner_table = None;
 
             for (column_index, (column, value)) in val.into_owned().into_iter().enumerate() {
-                let column_requested = columns.iter().find(|c| c.to_string() == column);
+                let column_requested = columns.iter().find(|c| c.to_column_name() == column);
                 let need_flatten = { columns.is_empty() || column_requested.is_some() };
                 let span = value.span();
 

crates/nu-command/src/filters/select.rs

@@ -240,7 +240,7 @@ fn select(
                                 //FIXME: improve implementation to not clone
                                 match input_val.clone().follow_cell_path(&path.members, false) {
                                     Ok(fetcher) => {
-                                        record.push(path.to_string(), fetcher);
+                                        record.push(path.to_column_name(), fetcher);
                                         if !columns_with_value.contains(&path) {
                                             columns_with_value.push(path);
                                         }
@@ -271,7 +271,7 @@ fn select(
                             // FIXME: remove clone
                             match v.clone().follow_cell_path(&cell_path.members, false) {
                                 Ok(result) => {
-                                    record.push(cell_path.to_string(), result);
+                                    record.push(cell_path.to_column_name(), result);
                                 }
                                 Err(e) => return Err(e),
                             }
@@ -295,7 +295,7 @@ fn select(
                         //FIXME: improve implementation to not clone
                         match x.clone().follow_cell_path(&path.members, false) {
                             Ok(value) => {
-                                record.push(path.to_string(), value);
+                                record.push(path.to_column_name(), value);
                             }
                             Err(e) => return Err(e),
                         }