Add support for v flag to regexp/prefer-character-class

[RunDevelopment]

Related to #545

Changes:

• What the title says.
• Added unicode-set.ts util file for reserved punctuators.
• Changed no-useless-character-class, no-useless-escape, and require-unicode-sets-regexp to use the new util file.

Some details about how I changed prefer-character-class:

• This rule assumes that character elements are exactly one character long. So it's hard to add support for e.g. \q{abc}. So I restricted it to character elements that don't contain strings. So the rule won't combine e.g. [abc]|[\q{abc}] -> [abc\q{abc}]. I think support for this can be added in a follow-up PR.
• Since the parsing with the v flag is stricter, I had to change elementsToCharacterClass (the function that creates the combined character class) to make more escapes. Those additional escapes apply to all regexes regardless of flags.

[changeset-bot]

🦋 Changeset detected

Latest commit: 2990bc5

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
eslint-plugin-regexp	Minor

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[ota-meshi]

LGTM! Thank you! I'm glad that the scattered code has been organized 😄