Editorial: refer to ECMA-262 as JavaScript rather than ECMAScript

This is consistent with how the HTML Living Standard refers to it and is how most developers would be familiar with it.

Included in this change:

- a note about this convention,
- renaming various algorithms and sections (and adding aliases for pre-existing IDs), and
- renaming variables and other things which refer to ECMAScript in an abbreviation.

Fixes #863.