Update XMLHandler

[kevin-mcgoldrick]

Update XMLHandler

Removes the jdom2 dependency and rewrites GenericXMLHandler on top of the JDK's built-in java.xml APIs (org.w3c.dom DOM + javax.xml XPath/Transformer). jdom2 is being dropped because the XML exception types it throws have been removed from the Java runtime.

What changed

• jdom2 removed from all POMs that declared it (pom.xml, agent_common, script_processor, web/web_ui).
• GenericXMLHandler rewritten using DOM / XPath / Transformer:
  • Read (GetElementText, GetElementAttr, GetElementList, xPathExists), write (SetElementText, SetElementAttribute, Save), and toString() reimplemented with no jdom2 types.
  • Create-on-write preserved — SetElementText/SetElementAttribute still build any missing path segments (and the root element) via a new resolveOrCreateElement helper, so XMLRequest can construct a body from an empty document as before.
• XXE hardening on the shared parser/transformer factories: disallow-doctype-decl, external general/parameter entities disabled, XInclude off, entity-reference expansion off, and external DTD/stylesheet access cleared on the transformer.
• Dead code removed — the empty JsonHandler / JsonHandlerTest classes are deleted.

Tests

• Replaced the disabled, auto-generated (@generatedBy CodePro) stubs in GenericXMLHandlerTest / XMLRequestTest with real assertions covering both the string- and file-based constructor paths, get/set of text & attributes, GetElementList, xPathExists (positive and negative), isXMLValid (valid + invalid), clone, and the path helpers.
• mvn clean test for agent_common is green.

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