RFR: 8354774: DocumentBuilderFactory getAttribute throws NPE

[Joe Wang]

Fix a NPE on calling DocumentBuilderFactory::getAttribute. This issue was found during the previous JCK test (JCK-7322355). The JCK failure was from a different method call, but it appears this is the root cause.

Also in this patch: consolidates get and set properties to use the same Util methods to reduce potential errors when code changes.

Test:
    Tier1 - 3 passed
    JCK test passed (will update JCK-7322355 once this patch is integrated)

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Commit messages:
 - 8354774: DocumentBuilderFactory getAttribute throws NPE

Changes: https://git.openjdk.org/jdk/pull/24732/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24732&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8354774
  Stats: 336 lines in 11 files changed: 220 ins; 67 del; 49 mod
  Patch: https://git.openjdk.org/jdk/pull/24732.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24732/head:pull/24732

PR: https://git.openjdk.org/jdk/pull/24732