[jdk17u-dev] RFR: 8282047: Enhance StringDecode/Encode microbenchmarks

[Boris Ulasevich]

This change is a backport of "8282047: Enhance StringDecode/Encode microbenchmarks" commit - a benchmarks update as a part of subsequent [JDK-8281146](https://bugs.openjdk.org/browse/JDK-8281146) change.

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Commit messages:
 - 8282047: Enhance StringDecode/Encode microbenchmarks

Changes: https://git.openjdk.org/jdk17u-dev/pull/666/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=666&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8282047
  Stats: 358 lines in 2 files changed: 218 ins; 71 del; 69 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/666.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev pull/666/head:pull/666

PR: https://git.openjdk.org/jdk17u-dev/pull/666