[jdk21u-dev] RFR: 8378353: [PPC64] StringCoding.countPositives causes errors when the length is not a proper 32 bit int

[Martin Doerr]

Backport of [JDK-8378353](https://bugs.openjdk.org/browse/JDK-8378353). Comment indentation changes don't apply to 21u. Besides that, the backport is clean.

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Commit messages:
 - Backport aee4b02ecdca43d66f4e0e4acc961e6efff56a6f

Changes: https://git.openjdk.org/jdk21u-dev/pull/2623/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2623&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378353
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2623.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2623/head:pull/2623

PR: https://git.openjdk.org/jdk21u-dev/pull/2623