RFR 8253451: Performance regression in java.util.Scanner after 8236201

[Martin Balao]

Hi,

I'd like to propose a fix for JDK-8253451 [1] performance regression.

Webrev.00:

 * http://cr.openjdk.java.net/~mbalao/webrevs/8253451/8253451.webrev.00

As explained in [1], the idea for the fix is to optimize the regexp
string for the most common group and decimal separator characters across
locales. Please note that there are a few locales where the proposed
optimization does not apply and the slower -but safe- regexp introduced
by 8236201 is used.

Testing:

 * No regressions observed in jdk/java/util/Scanner (5/5 passed)

 * Verified performance improvement back to what it was before 8236201
(on my Americas locale).

Thanks,
Martin.-

--
[1] - https://bugs.openjdk.java.net/browse/JDK-8253451