RFR: 8369190: JavaFrameAnchor on AArch64 appears to be missing barriers

[Justin King]

Add store barrier at the appropriate place in `JavaFrameAnchor::copy`. Move `sp` store to be last in `MacroAssembler::set_last_Java_frame`. Add `dmb ISHST` to `MacroAssembler::set_last_Java_frame` and `MacroAssembler::reset_last_Java_frame`.

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Commit messages:
 - Update comments
 - JDK-8369190: JavaFrameAnchor on AArch64 appears to be missing barriers

Changes: https://git.openjdk.org/jdk/pull/27645/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27645&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369190
  Stats: 22 lines in 2 files changed: 15 ins; 2 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/27645.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27645/head:pull/27645

PR: https://git.openjdk.org/jdk/pull/27645