`Regex.Match` element accessors should not materialize the whole output

[rxwei]

Currently Regex.Match element accessors are implemented this way:

  /// Lookup a capture by name or number
  public subscript<T>(dynamicMember keyPath: KeyPath<Output, T>) -> T {
    output[keyPath: keyPath]
  }

  // Allows `.0` when `Match` is not a tuple.
  @_disfavoredOverload
  public subscript(
    dynamicMember keyPath: KeyPath<(Output, _doNotUse: ()), Output>
  ) -> Output {
    output
  }

This is not correct as we should not materialize the entire output.

[milseman]

Is it possible to avoid the materialization?