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/strings/char_.rs

@@ -2,6 +2,7 @@ use indexmap::indexmap;
 use indexmap::map::IndexMap;
 use nu_engine::CallExt;
 use nu_protocol::engine::{EngineState, Stack};
+use nu_protocol::record;
 use nu_protocol::{
     ast::Call, engine::Command, Category, Example, IntoInterruptiblePipelineData, IntoPipelineData,
     PipelineData, ShellError, Signature, Span, SyntaxShape, Type, Value,
@@ -232,9 +233,6 @@ impl Command for Char {
             return Ok(CHAR_MAP
                 .iter()
                 .map(move |(name, s)| {
-                    let cols = vec!["name".into(), "character".into(), "unicode".into()];
-                    let name: Value = Value::string(String::from(*name), call_span);
-                    let character = Value::string(s, call_span);
                     let unicode = Value::string(
                         s.chars()
                             .map(|c| format!("{:x}", c as u32))
@@ -242,12 +240,13 @@ impl Command for Char {
                             .join(" "),
                         call_span,
                     );
-                    let vals = vec![name, character, unicode];
-                    Value::Record {
-                        cols,
-                        vals,
-                        span: call_span,
-                    }
+                    let record = record! {
+                        "name" => Value::string(*name, call_span),
+                        "character" => Value::string(s, call_span),
+                        "unicode" => unicode,
+                    };
+
+                    Value::record(record, call_span)
                 })
                 .into_pipeline_data(engine_state.ctrlc.clone()));
         }