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:

  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::pushs, 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}.