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-command/src/help/help_operators.rs

@@ -1,7 +1,8 @@
 use nu_protocol::{
     ast::Call,
     engine::{Command, EngineState, Stack},
-    Category, IntoInterruptiblePipelineData, PipelineData, ShellError, Signature, Type, Value,
+    record, Category, IntoInterruptiblePipelineData, PipelineData, ShellError, Signature, Type,
+    Value,
 };
 
 #[derive(Clone)]
@@ -35,23 +36,16 @@ impl Command for HelpOperators {
         let mut recs = vec![];
 
         for op in op_info {
-            let mut cols = vec![];
-            let mut vals = vec![];
-            cols.push("type".into());
-            vals.push(Value::string(op.op_type, head));
-            cols.push("operator".into());
-            vals.push(Value::string(op.operator, head));
-            cols.push("name".into());
-            vals.push(Value::string(op.name, head));
-            cols.push("description".into());
-            vals.push(Value::string(op.description, head));
-            cols.push("precedence".into());
-            vals.push(Value::int(op.precedence, head));
-            recs.push(Value::Record {
-                cols,
-                vals,
-                span: head,
-            })
+            recs.push(Value::record(
+                record! {
+                    "type" => Value::string(op.op_type, head),
+                    "operator" => Value::string(op.operator, head),
+                    "name" => Value::string(op.name, head),
+                    "description" => Value::string(op.description, head),
+                    "precedence" => Value::int(op.precedence, head),
+                },
+                head,
+            ));
         }
 
         Ok(recs