RFR: 8343629: More MergeStore benchmark [v3]

[Shaojin Wen]

> 1. Added the putBytes4 benchmark, which corresponds to StringBuilder appendNull
> 2. Optimized the putChars4/setInt/setLong series of benchmarks to reduce extra overhead and more accurately reflect performance differences.

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

  Update test/micro/org/openjdk/bench/vm/compiler/MergeStoreBench.java
  
  Co-authored-by: Emanuel Peter <emanuel.peter at oracle.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21659/files
  - new: https://git.openjdk.org/jdk/pull/21659/files/c6f05f20..4293ced9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21659&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21659&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21659.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21659/head:pull/21659

PR: https://git.openjdk.org/jdk/pull/21659