Summary of Changes

The UCM system was added in Joomla 3.2.0 and already at that time had major flaws. In 12 years of development, it hasn't been extended in any way and instead we've rather reduced it instead. (The content versioning was a part of it and has been made standalone in 4.0.) I think it can be said that the concept (which barely exists to start with) has failed and we should remove the remnants of it.
This PR deprecates all UCM classes that I could find. Unfortunately it does not yet remove all UCM usages in our core code, among other things because some of this is very deeply integrated into our classes. This mainly affects the tagging, which is built upon this feature. While I think this is very bad style, I'd like to deprecate this now, so that we can drop it in 7.0 and find replacements for everything in the meantime. The main goal would be to replace everything with better solutions in 6.0.

Testing Instructions

Codereview.

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed