RFR: 8339531: Improve performance of MemorySegment::mismatch [v10]

[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 incrementally with one additional commit since the last revision:

  Use unaligned ops and rename benchmarks

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20848/files
  - new: https://git.openjdk.org/jdk/pull/20848/files/e8d7777c..f40573c4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20848&range=09
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20848&range=08-09

  Stats: 19 lines in 4 files changed: 0 ins; 0 del; 19 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