Create Record type (#10103)

# Description
This PR creates a new `Record` type to reduce duplicate code and
possibly bugs as well. (This is an edited version of #9648.)
- `Record` implements `FromIterator` and `IntoIterator` and so can be
iterated over or collected into. For example, this helps with
conversions to and from (hash)maps. (Also, no more
`cols.iter().zip(vals)`!)
- `Record` has a `push(col, val)` function to help insure that the
number of columns is equal to the number of values. I caught a few
potential bugs thanks to this (e.g. in the `ls` command).
- Finally, this PR also adds a `record!` macro that helps simplify
record creation. It is used like so:
   ```rust
   record! {
       "key1" => some_value,
       "key2" => Value::string("text", span),
       "key3" => Value::int(optional_int.unwrap_or(0), span),
       "key4" => Value::bool(config.setting, span),
   }
   ```
Since macros hinder formatting, etc., the right hand side values should
be relatively short and sweet like the examples above.

Where possible, prefer `record!` or `.collect()` on an iterator instead
of multiple `Record::push`s, since the first two automatically set the
record capacity and do less work overall.

# User-Facing Changes
Besides the changes in `nu-protocol` the only other breaking changes are
to `nu-table::{ExpandedTable::build_map, JustTable::kv_table}`.

crates/nu-parser/src/eval.rs

@@ -1,7 +1,7 @@
 use nu_protocol::{
     ast::{Expr, Expression},
     engine::StateWorkingSet,
-    ParseError, Span, Value,
+    ParseError, Record, Span, Value,
 };
 
 /// Evaluate a constant value at parse time
@@ -59,28 +59,22 @@ pub fn eval_constant(
             })
         }
         Expr::Record(fields) => {
-            let mut cols = vec![];
-            let mut vals = vec![];
+            let mut record = Record::new();
             for (col, val) in fields {
                 // avoid duplicate cols.
                 let col_name = value_as_string(eval_constant(working_set, col)?, expr.span)?;
-                let pos = cols.iter().position(|c| c == &col_name);
+                let pos = record.cols.iter().position(|c| c == &col_name);
                 match pos {
                     Some(index) => {
-                        vals[index] = eval_constant(working_set, val)?;
+                        record.vals[index] = eval_constant(working_set, val)?;
                     }
                     None => {
-                        cols.push(col_name);
-                        vals.push(eval_constant(working_set, val)?);
+                        record.push(col_name, eval_constant(working_set, val)?);
                     }
                 }
             }
 
-            Ok(Value::Record {
-                cols,
-                vals,
-                span: expr.span,
-            })
+            Ok(Value::record(record, expr.span))
         }
         Expr::Table(headers, vals) => {
             let mut output_headers = vec![];
@@ -97,11 +91,13 @@ pub fn eval_constant(
                 for expr in val {
                     row.push(eval_constant(working_set, expr)?);
                 }
-                output_rows.push(Value::Record {
-                    cols: output_headers.clone(),
-                    vals: row,
-                    span: expr.span,
-                });
+                output_rows.push(Value::record(
+                    Record {
+                        cols: output_headers.clone(),
+                        vals: row,
+                    },
+                    expr.span,
+                ));
             }
             Ok(Value::List {
                 vals: output_rows,