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-cmd-dataframe/src/dataframe/eager/list.rs

@@ -1,7 +1,7 @@
 use nu_protocol::{
     ast::Call,
     engine::{Command, EngineState, Stack},
-    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Value,
+    record, Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Value,
 };
 
 use crate::dataframe::values::NuDataFrame;
@@ -55,27 +55,14 @@ impl Command for ListDF {
                 NuDataFrame::try_from_value(value).ok().map(|df| (name, df))
             })
             .map(|(name, df)| {
-                let name = Value::String {
-                    val: name,
-                    span: call.head,
-                };
-
-                let columns = Value::int(df.as_ref().width() as i64, call.head);
-
-                let rows = Value::int(df.as_ref().height() as i64, call.head);
-
-                let cols = vec![
-                    "name".to_string(),
-                    "columns".to_string(),
-                    "rows".to_string(),
-                ];
-                let vals = vec![name, columns, rows];
-
-                Value::Record {
-                    cols,
-                    vals,
-                    span: call.head,
-                }
+                Value::record(
+                    record! {
+                        "name" => Value::string(name, call.head),
+                        "columns" => Value::int(df.as_ref().width() as i64, call.head),
+                        "rows" => Value::int(df.as_ref().height() as i64, call.head),
+                    },
+                    call.head,
+                )
             })
             .collect::<Vec<Value>>();
 

crates/nu-cmd-dataframe/src/dataframe/eager/to_nu.rs

@@ -2,7 +2,7 @@ use nu_engine::CallExt;
 use nu_protocol::{
     ast::Call,
     engine::{Command, EngineState, Stack},
-    Category, Example, PipelineData, ShellError, Signature, Span, SyntaxShape, Type, Value,
+    Category, Example, PipelineData, Record, ShellError, Signature, Span, SyntaxShape, Type, Value,
 };
 
 use crate::dataframe::values::NuExpression;
@@ -40,21 +40,18 @@ impl Command for ToNu {
 
     fn examples(&self) -> Vec<Example> {
         let cols = vec!["index".into(), "a".into(), "b".into()];
-        let rec_1 = Value::Record {
+        let rec_1 = Value::test_record(Record {
             cols: cols.clone(),
             vals: vec![Value::test_int(0), Value::test_int(1), Value::test_int(2)],
-            span: Span::test_data(),
-        };
-        let rec_2 = Value::Record {
+        });
+        let rec_2 = Value::test_record(Record {
             cols: cols.clone(),
             vals: vec![Value::test_int(1), Value::test_int(3), Value::test_int(4)],
-            span: Span::test_data(),
-        };
-        let rec_3 = Value::Record {
+        });
+        let rec_3 = Value::test_record(Record {
             cols,
             vals: vec![Value::test_int(2), Value::test_int(3), Value::test_int(4)],
-            span: Span::test_data(),
-        };
+        });
 
         vec![
             Example {
@@ -76,11 +73,10 @@ impl Command for ToNu {
             Example {
                 description: "Convert a col expression into a nushell value",
                 example: "dfr col a | dfr into-nu",
-                result: Some(Value::Record {
+                result: Some(Value::test_record(Record {
                     cols: vec!["expr".into(), "value".into()],
                     vals: vec![Value::test_string("column"), Value::test_string("a")],
-                    span: Span::test_data(),
-                }),
+                })),
             },
         ]
     }