[jdk9] RFR: 8160264 : Reuse Latin1/UTF16 compare routines

[Ivan Gerasimov]

Hello everyone!

StringLatin1 and StringUTF16 helper classes have a few very symmetric 
methods for comparing.
If we reuse them, it will save us a few bytes of generated bytecode.

Would you please help review this?

BUGURL: https://bugs.openjdk.java.net/browse/JDK-8160264
WEBREV: http://cr.openjdk.java.net/~igerasim/8160264/00/webrev/

With kind regards,
Ivan