RFR: 8196334: Optimize UUID#fromString

[Claes Redestad]

Hi all,

please review this patch to optimize UUID#fromString.

Jon Chambers originally proposed a patch that used a strict parser to
get a similar speed-up, but I failed to adapt it in a way that
could fall back to the less strict behavior while maintaining a
reasonable speed-up in the fast-path case. Sorry, Jon!

The patch proposed here was recently contributed by Andriy Plokhotnyuk
(OCA signed), and manages to get more than a 3x speed-up on the new
fromString microbenchmark, while falling back gently to the current,
less strict implementation if ever needed. I've done some light edits,
and added a simple microbenchmark.

Bug:    https://bugs.openjdk.java.net/browse/JDK-8196334
Webrev: http://cr.openjdk.java.net/~redestad/8196334/open.00/

Testing: tier1-3

Thanks!

/Claes