RFR: 8334342: Add MergeStore JMH benchmarks [v6]

[Chen Liang]

On Thu, 18 Jul 2024 00:52:17 GMT, Shaojin Wen <duke at openjdk.org> wrote:

>> [8318446](https://github.com/openjdk/jdk/pull/16245)  brings MergeStore. We need a JMH Benchmark to evaluate the performance of various batch operations and the effect of MergeStore.
>
> Shaojin Wen has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 14 additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'upstream/master' into merge_store_bench
>  - Merge remote-tracking branch 'upstream/master' into merge_store_bench
>  - bug fix for `putChars4C`
>  - bug fix for `putChars4C` and `putChars4S`
>  - use VarHandler CHAR_L & CHAR_B
>  - copyright
>  - bug fix for putIntBU
>  - add cases for `getChar` & `putChar`
>  - code format
>  - add `setIntRL` & `setIntRLU`
>  - ... and 4 more: https://git.openjdk.org/jdk/compare/1bd72368...74f8837c

Should we leave this benchmark in `vm/compiler` instead of `java/lang`?

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PR Comment: https://git.openjdk.org/jdk/pull/19734#issuecomment-2247951444