RFR: 8352316: More MergeStoreBench [v7]

[Shaojin Wen]

> Added performance tests related to String.getBytes/String.getChars/StringBuilder.append/System.arraycopy in constant scenarios to verify whether MergeStore works

Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:

  add StringBuilderUnsafePut

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24108/files
  - new: https://git.openjdk.org/jdk/pull/24108/files/322624eb..cd1d8fb3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24108&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24108&range=05-06

  Stats: 245 lines in 1 file changed: 211 ins; 0 del; 34 mod
  Patch: https://git.openjdk.org/jdk/pull/24108.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24108/head:pull/24108

PR: https://git.openjdk.org/jdk/pull/24108