ImageScale.tag populates alt and title with same content

[thet]

According to WAI standards from my understanding, the alt and title should not contain the same content - both are read aloud by screen readers.

In plone.namedfile.scaling.ImageScale.tag the alt and title attribute are set to the image title (self.title)‌ if both are empty: https://github.com/plone/plone.namedfile/blob/master/plone/namedfile/scaling.py#L157

This is wrong and should be fixed.

There is the alt-tag-behavior issue/PR plone/plone.app.contenttypes#700 which aims to add a behavior for images to edit alt tags. We should jump on that and fix this issue together with the other one.