[jdk11u-dev] RFR: 8279833: Loop optimization issue in String.encodeUTF8_UTF16

[Goetz Lindenmaier]

I backport this for parity with 11.0.15-oracle.

The patch does not apply well.

8259842: Remove Result cache from StringCoding  is missing in 11.
Therefore the actual change must be applied to StringCoding.java
and not to String.java.  The method encodeUTF8_UTF16() was moved
from the one to the other file in 8259842.

8259842 change also brought the benchmark edited by this change.
I include the whole benchmark in this change.

-------------

Commit messages:
 - Backport ff8565931115d581afff679ea85b1a2d80c03b99

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/791/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=791&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279833
  Stats: 132 lines in 2 files changed: 128 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/791.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/791/head:pull/791

PR: https://git.openjdk.java.net/jdk11u-dev/pull/791