[jdk21u] RFR: 8309502: RISC-V: String.indexOf intrinsic may produce misaligned memory loads

[Vladimir Kempik]

Clean backport to jdk21u

Significantly Improves performance of intrinsic in some cases for String.indexOf on platforms withotu hardware misaligned memory acccess support

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Commit messages:
 - Backport 6b942893868fa1a64977288bdbdb1bbff8bd9d9c

Changes: https://git.openjdk.org/jdk21u/pull/2/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=2&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309502
  Stats: 84 lines in 3 files changed: 67 ins; 5 del; 12 mod
  Patch: https://git.openjdk.org/jdk21u/pull/2.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/2/head:pull/2

PR: https://git.openjdk.org/jdk21u/pull/2