[Feature]: support regex alternation `/a|b/`

[SKalt]

Rationale

Extends ECMAScript Regular expression support

Actual behavior

import { RecognizePattern } from "."
import { Eq } from "./utils"
const topLevelAlternationAOk = Eq<RecognizePattern<"a|b", "a">, "a"> = true
const topLevelAlternationBOk = Eq<RecognizePattern<"a|b", "b">, "b"> = true