[jdk18] RFR: 8278627: Shenandoah: TestHeapDump test failed

[Zhengyu Gu]

This intermittent failure seems to be observed only on Linux ppc64le, but it is **not** ppc specific problem.

With concurrent thread stack scanning/updating, nmtehod entry barrier has to be applied prior to thread stack/code roots scanning during heap iteration, to ensure scanner only sees to-space objects.

The patch also cleanup the use of `nmethod::oops_do_marking_prologue/epilogue()`, which should be used with `nmethod::oops_do_try_claim()` and closures that use the nmethod, e.g. `MarkingCodeBlobClosure`. Since `Shenandoah` switched to concurrent code root iteration, they are no longer applied.

Test:
The failure on Linux ppc64le is intermittent, usually sees a failure about 3 `hotspot_gc_shenandoah` runs. I have yet seen any failures after 10 runs with the patch.

SAP tested this patch in jdk/jdk repo in nightly tests, did not see failure so far.

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Commit messages:
 - 8278627: Shenandoah: TestHeapDump test failed

Changes: https://git.openjdk.java.net/jdk18/pull/56/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18&pr=56&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278627
  Stats: 56 lines in 3 files changed: 23 ins; 6 del; 27 mod
  Patch: https://git.openjdk.java.net/jdk18/pull/56.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18 pull/56/head:pull/56

PR: https://git.openjdk.java.net/jdk18/pull/56