[jdk21] RFR: 8313809: String template fails with java.lang.StringIndexOutOfBoundsException if last fragment is UTF16

[Jim Laskey]

8313809: String template fails with java.lang.StringIndexOutOfBoundsException if last fragment is UTF16

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Commit messages:
 - Backport 6864441163f946d0bec7380a2a120e31b812a6dc

Changes: https://git.openjdk.org/jdk21/pull/170/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21&pr=170&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313809
  Stats: 49 lines in 2 files changed: 45 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk21/pull/170.diff
  Fetch: git fetch https://git.openjdk.org/jdk21.git pull/170/head:pull/170

PR: https://git.openjdk.org/jdk21/pull/170