fix: declare java.xml module dependency for Java 9+ modular usage

[JinlongLiao]

What this PR does / why we need it?

This PR fixes the IllegalAccessError that occurs when using fastjson2 (v2.0.61) in Java 9+ modular environments. The error is caused by missing java.xml module declaration in src/main/moditect/module-info.java, while the code internally references org.w3c.dom.Node from java.xml.

Without this fix, users cannot properly use fastjson2 in modularized projects, as the JVM prevents access to java.xml classes.

Summary of your change

• Updated src/main/moditect/module-info.java to explicitly declare requires java.xml;.
• Ensured that ObjectWriterProvider and related XML handling code can access org.w3c.dom.Node without IllegalAccessError.
• Verified compatibility with Java 9+ modular projects.
• Added regression tests to confirm XML serialization works under modularized environments.

Please indicate you've done the following:

• Made sure tests are passing and test coverage is added if needed.
• Made sure commit message follow the rule of Conventional Commits specification.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ JinlongLiao
❌ jinlongliao

---

jinlongliao seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[wenshao]

No issues found. LGTM! ✅ — gpt-5.5 via Qwen Code /review

[yaozhihang]

Hi, will this PR be merged soon for the next release?

[wenshao]

LGTM ✅

The requires java.xml; declaration is correct and necessary — ObjectWriterImplXmlNode and ObjectWriterProvider both directly reference org.w3c.dom.Node and javax.xml.transform.* types from the java.xml module. Non-transitive requires is the right choice since these types are only used internally and do not leak into the exported public API.

— qwen3.7-max via Qwen Code /review

[wenshao]

No issues found. LGTM! ✅

— qwen3.8-max-preview via Qwen Code /review