Editorial: Refactor Parse operations (#2244)

* Add structured headers.
* Consistently employ ParseText.
* Consistently check parse results for Parse Nodes rather than productions.
* Consistently read and interact with code points from Parse Nodes ("source text matched by" or "an empty sequence" fallbacks) rather than strings/code units.
* Correctly use CodePointsToString for conversion.
* Create new "MV" aliases rather than replacing text/string values.
* Always use the same approach when reading fraction components:
  1. substring of CodePointsToString(…) from 1
  2. string-concatenation with *"000000000"*
  3. substring
  4. ToIntegerOrInfinity

Author: gibson042