Convert Java from Docbook to CommonMark

[ryantm]

This issue tracks the conversion of /doc/languages-frameworks/java.xml from Docbook to CommonMark per RFC 72.

If you intend to work on this conversion, please comment below!

Instructions for performing this conversion

1. Post in this issue that you intend to work on it. (Please also post if you stop working on it)
2. Checkout a new branch of nixpkgs master.
3. Edit doc/languages-frameworks/index.xml: change java.xml to java.section.xml.
4. Move doc/languages-frameworks/java.xml to doc/languages-frameworks/java.section.md.
5. Convert the contents from Docbook to CommonMark. Use existing .md sections for inspiration.
6. Use nix-build from the doc/ folder to build the manual.
7. Preview the manual on your computer at http://0.0.0.0:8000/manual.html after running from doc/ folder:

nix-shell -p python3 --run 'python3 -m http.server --directory ./result/share/doc/nixpkgs'

8. When it looks good, submit a PR and reference this issue.

[Mic92]

#105230