[jdk20u] RFR: 8301491: C2: java.lang.StringUTF16::indexOfChar intrinsic called with negative character argument

[Tobias Hartmann]

Backport of [JDK-8301491](https://bugs.openjdk.java.net/browse/JDK-8301491). Applies cleanly. Approval is pending.

Thanks,
Tobias

-------------

Commit messages:
 - 8301491: C2: java.lang.StringUTF16::indexOfChar intrinsic called with negative character argument

Changes: https://git.openjdk.org/jdk20u/pull/42/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk20u&pr=42&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301491
  Stats: 85 lines in 2 files changed: 83 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk20u/pull/42.diff
  Fetch: git fetch https://git.openjdk.org/jdk20u.git pull/42/head:pull/42

PR: https://git.openjdk.org/jdk20u/pull/42