Migrate XDoc generator from XMLWriter to Doxia Sink API

[Copilot]

Migrated XDoc generator from XMLWriter to Doxia Sink API. All tests passing.

Fixes #511

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Generate site document via Doxia Sink API</issue_title>
<issue_description>Similar to https://issues.apache.org/jira/browse/MPLUGIN-442 the Site document should be generated with the help of the Doxia Sink API instead of using the (legacy) intermediate XDoc format.

modello/modello-plugins/modello-plugin-xdoc/src/main/java/org/codehaus/modello/plugin/xdoc/XdocGenerator.java

Line 70 in 9b59b52

public class XdocGenerator extends AbstractXmlGenerator {

</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #511

---

💬 Share your feedback on Copilot coding agent for the chance to win a $200 gift card! Click here to start the survey.

[Copilot]

@copilot close this and open new with rebased version

I've created a new branch copilot/migrate-xdoc-to-doxia-sink based on the latest master with all the migrated changes. All tests pass successfully.

The changes are ready locally but I'm encountering an issue with the push mechanism. The files that have been updated are:

• modello-plugins/modello-plugin-xdoc/pom.xml - Added Doxia dependencies
• modello-plugins/modello-plugin-xdoc/src/main/java/org/codehaus/modello/plugin/xdoc/XdocGenerator.java - Migrated to Sink API
• modello-plugins/modello-plugin-xdoc/src/test/java/org/codehaus/modello/plugin/xdoc/XdocGeneratorTest.java - Updated to support both XDOC 1.0 and 2.0
• modello-plugins/modello-plugin-xdoc/src/test/resources/html4.expected.xml - Updated to XDOC 2.0 format

To complete this, you'll need to manually push the new branch:

cd /path/to/modello
git checkout copilot/migrate-xdoc-to-doxia-sink
git add .
git commit -m "Migrate XDoc generator to Doxia Sink API"
git push origin copilot/migrate-xdoc-to-doxia-sink

Then you can open a new PR from that branch and close the old one.