RFR: 8339531: Improve performance of MemorySegment::mismatch [v11]

[Per Minborg]

> This PR proposes to improve the performance of `MemorySegment::mismatch` by using Java code rather than transitioning to native code.

Per Minborg 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 22 additional commits since the last revision:

 - Always use Java for mismatch by default on a64
 - Only use unrolling on a64
 - Unroll loop and move method
 - Merge branch 'master' into mismatch-performance2
 - Use unaligned ops and rename benchmarks
 - Fix errors in a benchmark
 - Lower the mismatch threshold
 - Move method to SegmentBulkOperations and fix benchmark
 - Merge branch 'master' into mismatch-performance2
 - Consolidate logic in one method
 - ... and 12 more: https://git.openjdk.org/jdk/compare/9f3c9169...a75dc159

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20848/files
  - new: https://git.openjdk.org/jdk/pull/20848/files/f40573c4..a75dc159

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20848&range=10
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20848&range=09-10

  Stats: 9514 lines in 321 files changed: 5283 ins; 2651 del; 1580 mod
  Patch: https://git.openjdk.org/jdk/pull/20848.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20848/head:pull/20848

PR: https://git.openjdk.org/jdk/pull/20848