[forms] Fix edition of TZDatetime attributes Parse the submitted web form values into a timezone-aware datetime (by default, UTC) when such an attribute is edited. This is done using an automatically-selected (by `web.formfield.guess_field`) field named `TZDatetimeField`. Closes #12666598.

.. -*- coding: utf-8 -*-


Server Architecture
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.. image:: images/server-class-diagram.png

`Diagramme ArgoUML`_

[FIXME]
Make a downloadable source of zargo file.

.. _`Diagramme ArgoUML`: cubicweb.zargo