The refactoring of the wysiwyg editor and 'html' field allows us to
move some of the code that was in web_editor but only used in website or
in mass_mailing. Some parts are still in web_editor but will be
moved at a later time.

When an inline editor is eg. in a form view, the focus is always stolen
by it.

This is because we trigger a mouseup on the editor to update its
toolbars values and informations.

In 10.0 this was not necessary since the default values were sanely set
when the editor was inside the DOM. In 11.0 the editor is not in the DOM
when this is being done and the info was wrong (eg. NaN for text size).

With this commit, we don't steal the focus and get the default like it
was done in 10.0 instead.

fixes #26366
opw-1874880
closes #26582

Before this fix, the attachments are don't save to the record and are
remove with the wizard. We can't add the attachments to mail.message
(like 'mail.compose.message') because it's auto_delete/unlink and the
attachments are removed before the recipient can read it.

Before this fix attachmentThumbnailToLinkImg is not called for
style-inline options. The mail received does not have thumbnail and the
user can't click on the invisible link.

opw-1863659

Commit 6494f511718 introduces an access token to read images inside an
email. This avoids access errors when accessing the email through a
proxy (e.g. Gmail). That implies that all images are added as
attachments.

When going through the usual media dialog, the form is submitted to
action '/web_editor/attachment/add', creating the attachment. However,
the copy or the drag and drop of an image completely fails. Indeed,
the same method `_onImageUpload` is called, but with a completely
different argument type: `attachments` is a `FileList`, not a list of
attachments.

To solve this, we only call `_onImageUpload` on a the custom `onUpload`
callback, which is not triggered during a drag and drop or a copy. Any
image included thanks to these methods will be post-processed in the
`create` method of `mail.message` (`base64_to_boundary`).

Unfortunately, it's not possible to simulate an actual drag and drop or
a copy, so we cannot add a test.

opw-1840237
opw-1840411