When a checklist is present in an html field, there is a feature that
allows us to check/uncheck its boxes without going through edit mode.
That feature was broken due to a dead callback in wysiwyg.js, which is
hereby restored.
Meanwhile, the behaviour of checklists had changed but the python code
handling the readonly checking/unchecking hadn't so this brings it up to
date[1].
Finally, the code managing checklist ids was unnecessarily complicated
as it was trying to keep the ids consecutive for no particular reason.
This refactors it to simply use unique ids based on date stamps.
[1] It used to be that checking a box checked all the children of that
box but it was in the meantime decided not to do that anymore.
Part-of: odoo/odoo#81920
Antoine Guenet
41e98ccbe4