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

[Vladimir Kempik]

Please review this attempt to remove misaligned loads in String.indexOf intrinsic on RISC-V

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Commit messages:
 - Initial fix

Changes: https://git.openjdk.org/jdk/pull/14320/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14320&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309502
  Stats: 18 lines in 1 file changed: 14 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/14320.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14320/head:pull/14320

PR: https://git.openjdk.org/jdk/pull/14320