jrjackson fails to parse valid JSON in UTF-16 and UTF-32

[yaauie]

8.1. Character Encoding

JSON text SHALL be encoded in UTF-8, UTF-16, or UTF-32. The default
encoding is UTF-8, and JSON texts that are encoded in UTF-8 are
interoperable in the sense that they will be read successfully by the
maximum number of implementations; there are many implementations
that cannot successfully read texts in other encodings (such as
UTF-16 and UTF-32).

-- RFC7159 §8.1

[yaauie]

There are at least two layers of failure here, which is why I'm submitting this as a failing-tests PR instead of coming to a solution.

1. JrJackson::Json::is_time_string?(Str) encounters an exception in the Regexp library if the given string's encoding isn't ASCII-compatible, since the regexp is ASCII.
2. if we attempt to fall through to UTF-16 or UTF-32, and have appropriate regexp built for these cases, parsing fails in super weird ways, re-emitting previously-captured yet unrelated tokens.