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

[Goetz Lindenmaier]

I backport this for parity with 17.0.18-oracle.

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Commit messages:
 - Backport d4d12ad1d92ae6d353ce9e16b1b72e6416874cd6

Changes: https://git.openjdk.org/jdk17u-dev/pull/4011/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=4011&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/4011.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/4011/head:pull/4011

PR: https://git.openjdk.org/jdk17u-dev/pull/4011