[jdk18] RFR: 8278186: throw StringIndexOutOfBoundsException when calling substring method

[Weijun Wang]

Add check on `xpointer(id('name'))` format.

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Commit messages:
 - 8278186: throw StringIndexOutOfBoundsException when calling substring method

Changes: https://git.openjdk.java.net/jdk18/pull/1/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18&pr=1&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278186
  Stats: 75 lines in 4 files changed: 66 ins; 0 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk18/pull/1.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18 pull/1/head:pull/1

PR: https://git.openjdk.java.net/jdk18/pull/1