Refs. commits message for steps to reproduce

COMMIT 1:
----------------

Issue:
------

One attachment has been removed (not linked anymore to the move).

Cause:
------

When switching the main attachment, the versioning is triggered; the
new main attachment is set on the document and the previous is added
to the history for versioning (and therefore also change the res fields
to be linked to the document instead of the move).

Solution:
---------

When updating the attachment of a document that already have an
attachment (normal versioning), we should remove the link between the
current document attachment (not the new one) and the related model
only if the related model has not a `message_main_attachment_id` field
or if the current document attachment is different of the main
attachment set on the related model.

COMMIT 2:
----------------

Issue:
------

A second document is created.

Cause:
------

The issue is when switching the second time the invoice main attachment,
the current main attachment is in fact in the versioned attachments
(`document.preview_attachment_ids`), and since we search only for
document that have as attachment (`document.attachment_id`) the
current invoice main attachment, we don't find it and create a new
document.

Solution:
---------

Look also in the versioned attachments when searching for the invoice
main attachment in case it has been versioned.

opw-4028789

Forward-Port-Of: odoo/enterprise#67464
Forward-Port-Of: odoo/enterprise#66501