Add `require-unicode-sets-regexp`

[Michael Schmidt]

Same as the require-unicode-regexp rule, but for the v flag.

Auto fixing should work the same as for require-unicode-regexp. We will only have a fix if we can prove that adding the v flag doesn't change the behavior of the regex.

Note: It might be difficult to migrate from legacy (no u or v flag) to the v flag in one step. We should probably migrate the u (if not present already) first.