Refactor reference data into groups

[jeddy3]

Which issue, if any, is this issue related to?

• Follows on from @ybiquitous great work in Add shorthand properties reference to public API #6168
• Original issue Publicly expose reference data #6151

Is there anything in the PR that needs further explanation?

This pull request doesn't add any new reference data to the public API as we'll only want to do that if it's requested because we'll need to make sure the set names are accurate to the specs. What it does is:

• breaks up the unwieldy keywordSet.js file into more accurately named groups
• uses the destructuring convention from Add shorthand properties reference to public API #6168 to make it clear what data a rule or util is using
• standardizes a few of the set names, e.g. everything in keywords is a *Keywords set

Hopefully, this will make the reference data easier to work with internally and better prepare it for being added to the public API when requested.

[ybiquitous]

This is great work! I've left trivial suggestions, but it looks good enough to merge. 👍🏼