- If a deprecate parameter is in use in the wikitext (no matter if it does have a value or not), show it in the sidebar.
- For deprecated parameters not in use, hide them in the sidebar so that they cannot be added.
- Removing a deprecated parameter does not immediately remove it's entry in the sidebar. The behavior should be similar to an undocumented parameter.
- Make sure we never create a dirty diff on save.
Note: Deprecated parameters will be prevented from being added through the undocumented parameter input, added in T272487: New input for undocumented parameters. This is covered in the related ticket about error handling, see T285869: Add error handling for the undocumented parameter input.