DSL quantifier types -> quantifier functions

[rxwei]

Change quantifiers in the DSL from structure types to top-level functions. This allows for a lot more flexibility with overloading a quantifier based on the input Match type. The immediate benefit of this is getting rid of void and nested void types (see example below), and as a result eliminate the need for void-filtering within concatenation. A more important benefit (IMO) is being able to get rid of nominal tuples and switch back to Swift tuples, as Swift tuples enable strongly typed named captures and eliminates the complexity that comes with nominal tuples.

This PR is based on #114. Please review commit b14a85b.

---

Before:

let r0 = OneOrMore(.digit) // => `.Match == Tuple2<Substring, [()]>`
let r1 = Optionally(.digit) // => `.Match == Tuple2<Substring, ()?>`
let r2 = OneOrMore(Repeat(Optionally(.digit))) // => `.Match == Tuple2<Substring, [[()?]]>`
"123".match(r2) // => `RegexMatch<Tuple2<Substring, [[()?]]>>?`

After:

let r0 = oneOrMore(.digit) // => `.Match == Substring`
let r1 = optionally(.digit) // => `.Match == Substring`
let r2 = oneOrMore(many(optionally(.digit))) // => `.Match == Substring`
"123".match(r2) // => `RegexMatch<Substring>`

---

Before:

/(?<number>\d+)/ // => `Regex<Tuple2<Substring, Substring>>`

After:

/(?<number>\d+)/ // => `Regex<(Substring, number: Substring)>`

[rxwei]

@swift-ci please test Linux

[milseman]

Is this the PR that drops the nominal public types, or a different one?

[milseman]

Ah, are we dropping them for literal but not result builder?

[rxwei]

The public types, e.g. Concatenation_0_1, will be dropped in a follow-up PR.

[milseman]

@swift-ci please test linux platform

[milseman]

LGTM

[rxwei]

@swift-ci please test Linux