RFR: 8354084: Streamline XPath API's extension function control

[Joe Wang]

Streamline the extension function control in the XPath API by relying solely on [XPathFunctionResolver](https://docs.oracle.com/en/java/javase/24/docs/api/java.xml/javax/xml/xpath/XPathFunctionResolver.html), which provides a secure and developer-defined mechanism. Remove the feature FEATURE_SECURE_PROCESSING and jdk.xml.enableExtensionFunctions from the decision path that are redundant with regard to XPath's Extension Functions.

Note the comment in JAXPExtensionsProvider, starting at  "JAXP 1.3 spec says When ...", was not accurate. Refer to the spec: https://docs.oracle.com/en/java/javase/24/docs/api/java.xml/javax/xml/XMLConstants.html#FEATURE_SECURE_PROCESSING, FSP does not have specific requirement for the XPath functions.

Tests:
    Tier1 - 3 passed with regard to this change. There were unrelated/known failures (e.g. bug8329757).
    JCK passed except the previously reported issue (JCK-7322355).

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Commit messages:
 - 8354084: Streamline XPath API's extension function control

Changes: https://git.openjdk.org/jdk/pull/24605/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24605&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8354084
  Stats: 516 lines in 19 files changed: 185 ins; 301 del; 30 mod
  Patch: https://git.openjdk.org/jdk/pull/24605.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24605/head:pull/24605

PR: https://git.openjdk.org/jdk/pull/24605