Mark CKEditor 4 functions as deprecated

[NormPlum]

When searching for CKEditor hooks/functions, there are results for both CKEditor (4) and CKEditor 5:

Since CKEditor 4 is deprecated, can we add a note to those functions explaining this and pointing to the appropriate CKEditor 5 function instead?

E.g.: https://docs.backdropcms.org/api/backdrop/core!modules!ckeditor!ckeditor.api.php/function/hook_ckeditor_plugins/1

This is a link to the Docs site, but I believe this information comes from core.