LO/OO: Persist in-text/empty nature in the CSL reference mark

[pluto-han]

This is the follow-up issue of #15370 and Embed in-text nature in reference marks for CSL citations, which extends the solution to invisible(empty) citations.

This issue involves two parts:

1. Use enum (e.g. CITATION_TYPE{NORMAL, IN_TEXT, EMPTY}) to replace boolean var in the method signature.
2. Redesign and re-implement reference mark format, as well as the parsing logic.

[pluto-han]

Issue type should be "Feature" instead of "Bug"

[github-actions]

A pull request addressing the issue has been created. You can try out the pull request by following the steps at How to try out any JabRef pull request?.

For any feedback, add a comment to the pull request at #15437.