[jdk17u-dev] RFR: 8279833: Loop optimization issue in String.encodeUTF8_UTF16

[Goetz Lindenmaier]

I backport this for parity with 17.0.3-oracle.

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Commit messages:
 - Backport c3d0a94040d9bd0f4b99da97b89fbfce252a41c0

Changes: https://git.openjdk.java.net/jdk17u-dev/pull/97/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u-dev&pr=97&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279833
  Stats: 88 lines in 2 files changed: 45 ins; 4 del; 39 mod
  Patch: https://git.openjdk.java.net/jdk17u-dev/pull/97.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u-dev pull/97/head:pull/97

PR: https://git.openjdk.java.net/jdk17u-dev/pull/97