RATIONALE

Event will soon gain a major update called Event Online, allowing to better
support full-online events. In order to prepare its merge, preparatory merge
are done to lessen the final diff and have a smooth integration in a stable
version (13.3).

PURPOSE

Purpose of this merge is to clean visitor synchronization and tests. It
prepares further improvements to visitor model linked to Event Online.

SPECIFICATIONS

Add anchor methods to somehow merge visitors and update partner linked
to visitors and their sub records.

Main idea would be to be able to

  * avoid unlinking visitors, notably because we have keys linked to them
    allowing push notifications. As a given user may be linked to several
    devices (different keys / different visitors) keeping them in database
    improves push efficiency;
  * allow to link sub-records to a main visitor, like tracked pages history,
    even if multiple visitors are linked to the same identity;

In this stable we cannot remove current unlink of duplicate visitors due
to constraint of partner_id / visitor_id. However those methods allow to
tweak behavior by override. This will be done in future tasks.

LINKS

Task ID 2290016 (improve visitor synchronization and tests)
Prepares Task ID 2252655 (main Online Event task)
Prepares Task ID 2284043 (Visitor-based track wishlist)
PR #54036

X-original-commit: 8a8d2d4412d1b58545ee4f0240cca5114e541b6a
Co-authored-by: Aurélien Warnon <awa@odoo.com>
Co-authored-by: David Beguin <dbe@odoo.com>
Co-authored-by: Thibault Delavallée <tde@odoo.com>