Be more strict when checking if mimetype is allowed inline

[mauritsvanrees]

This takes over some code from zopefoundation/Zope#1167

[mister-roboto]

@mauritsvanrees thanks for creating this Pull Request and helping to improve Plone!

TL;DR: Finish pushing changes, pass all other checks, then paste a comment:

@jenkins-plone-org please run jobs

To ensure that these changes do not break other parts of Plone, the Plone test suite matrix needs to pass, but it takes 30-60 min. Other CI checks are usually much faster and the Plone Jenkins resources are limited, so when done pushing changes and all other checks pass either start all Jenkins PR jobs yourself, or simply add the comment above in this PR to start all the jobs automatically.

Happy hacking!

[mauritsvanrees]

@jenkins-plone-org please run jobs

[gforcada]

LGTM! 👍🏾

Should we copy a test also from zope#1167 ?

    def test_extract_media_type(self):
        extract = OFS.Image.extract_media_type
        self.assertIsNone(extract(None))
        self.assertEqual(extract("text/plain"), "text/plain")
        self.assertEqual(extract("TEXT/PLAIN"), "text/plain")
        self.assertEqual(extract("text / plain"), "text/plain")
        self.assertEqual(extract(" text/plain ; charset=utf-8"), "text/plain")

And maintenance-wise, should we actually try to import first that function from Zope, and only if not there, use our own copy? So we can eventually drop our copied version? 🤔

[mauritsvanrees]

@gforcada Conditional import added, and test added.

@jenkins-plone-org please run jobs