RFR: 8364936: Shenandoah: Switch nmethod entry barriers to conc_instruction_and_data_patch [v3]

[Cesar Soares Lucas]

> Please, review this patch to make nmethod entry barriers use `conc-instruction-and-data-patch` fence mechanics when ShenandoahGC is being used on AArch64. The patch also removes (including from JVMCI interface) the old constant that was being used only by Shenandoah on AArch64.
> 
> The patch has been tested with functional and performance benchmarks on AArch64. Improvements in DaCapo and Renaissance benchmarks can be as high as 30%. Maximum critical Jops in SPEC improved by ~10%.

Cesar Soares Lucas has updated the pull request incrementally with one additional commit since the last revision:

  Make PPC backend to also use concurrent code patching.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26999/files
  - new: https://git.openjdk.org/jdk/pull/26999/files/3276b586..4da31385

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26999&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26999&range=01-02

  Stats: 3 lines in 2 files changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/26999.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26999/head:pull/26999

PR: https://git.openjdk.org/jdk/pull/26999