[jdk17u-dev] RFR: 8298087: XML Schema Validation reports an required attribute twice via ErrorHandler

[Goetz Lindenmaier]

I backport this for parity with 17.0.11-oracle.

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

Commit messages:
 - Backport 2179a8f2d622f832aa21eb7f48e8ab055bc55731

Changes: https://git.openjdk.org/jdk17u-dev/pull/1996/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1996&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298087
  Stats: 129 lines in 2 files changed: 123 ins; 4 del; 2 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1996.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1996/head:pull/1996

PR: https://git.openjdk.org/jdk17u-dev/pull/1996