Deprecate Xalan for removal

JMeter ships with Xalan, however, many its features are available with Java.
Xalan is not actively maintained, so we should consider removing Xalan APIs.

Unfortuantely, JMeter public APIs include Xalan classes, so we can't easily drop it.

The plan is as follows:
1) Deprecate Xalan for removal in JMeter 6.0 <-- this issue
2) Remove Xalan somewhere in 2026-2027

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Looks like `org.apache.jmeter.util.XPathUtil` is not used by third-party code:
https://github.com/search?q=%22import+org.apache.jmeter.util.XPathUtil%22&type=code

`org.apache.jmeter.util.PropertiesBasedPrefixResolver` is not used either:
https://github.com/search?q=%22import+org.apache.jmeter.util.PropertiesBasedPrefixResolver%22&type=code

Looks like we could just replace the implementation and drop Xalan