RFR: 8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier

[kuaiwei]

he origin patch for https://bugs.openjdk.org/browse/JDK-8324186 has 2 issues:
1 It show regression in some platform, like Apple silicon in mac os
2 Can not handle instruction sequence like "dmb.ishld; dmb.ishst; dmb.ishld; dmb.ishld"

It can be fixed by:
1 Enable AlwaysMergeDMB by default, only disable it in architecture we can see performance improvement (N1 or N2)
2 Check the special pattern and merge the subsequent dmb.

It also fix a bug when code buffer is expanding, st/ld/dmb can not be merged. I added unit tests for these.

This patch still has a unhandled case. Insts like "dmb.ishld; dmb.ishst; dmb.ish", it will merge the last 2 instructions and can not merge all three. Because when emitting dmb.ish, if merge all previous dmbs, the code buffer will shrink the size. I think it may break some resumption and think it's not a common pattern.

In previous PR https://github.com/openjdk/jdk/pull/18467 , I tried an implementation to use state machine for merging. But it looks risky to pending instruction during emitting.

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Commit messages:
 - 8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier

Changes: https://git.openjdk.org/jdk/pull/19278/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19278&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325821
  Stats: 343 lines in 9 files changed: 330 ins; 0 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/19278.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19278/head:pull/19278

PR: https://git.openjdk.org/jdk/pull/19278