RFR: JDK-8184947:,ZipCoder performance improvements

[Martin Buchholz]

Sorry, I haven't had the time I would like to review.
It would be good to make jdk10.
I keep wishing what we do for performance here wouldn't get so messy.
I keep thinking we should add some methods to the public Charset classes,
e.g. canDecode(byte[], int, int) with one general purpose implementation
and high-performance implementations for UTF-8, ASCII, Latin1
ASCII checking via hasNegatives has some hotspot help and that should be
available as a high performance public API somewhere.  One possibility is
my canDecode suggestion.

+            if (b >= 0)
+                putChar(dst, dp++, (char)b);
+            else
+                putChar(dst, dp++, repl);

why not coalesce into putChar(dst, dp++, (b >= 0) ? (char)b : repl)