Creating a `ChoiceOf` from an array

[bbrk24]

Relevant forums thread: https://forums.swift.org/t/creating-a-regex-choiceof-from-an-array/68755

I don't mind whether this is ChoiceOf.init<T: Collection<Substring>>(_ arr: T) or AlternationBuilder.buildArray<R: RegexComponent<Substring>>(_ components: [R]), but it should be possible to create a ChoiceOf from a collection.

[tomabuct]

+1