`CharacterClass.any` doesn't match newlines

[Hamish Knight]

https://github.com/apple/swift-evolution/blob/main/proposals/0363-unicode-for-string-processing.md states that:

  /// This character class is equivalent to the regex syntax "dot"
  /// metacharacter in single-line mode: `(?s:.)`.
  public static var any: CharacterClass { get }

however the following:

Regex {
  CharacterClass.any
}

does not match against a newline input.

rdar://96509234