RFR: 8354084: Streamline XPath API's extension function control [v4]

[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).

Joe Wang has updated the pull request incrementally with one additional commit since the last revision:

  update javadoc for the jdk.xml.enableExtensionFunctions property

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24605/files
  - new: https://git.openjdk.org/jdk/pull/24605/files/c7ec55a1..4f26a489

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24605&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24605&range=02-03

  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 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