[FIX] base: upsert translations during copy_translations

When doing a copy, create the new translations directly in SQL and handle
potential conflicts.

Conflicts can occure in case of reinstallation as showed in opw-1955062 and
opw-1950117.
In case of "leftovers" of translations (e.g. remaining after the uninstallation
of a module), creating the new translations (when reinstalling the module) may
produce a conflict with (type, name, res_id, lang) and raise an error.

This is NOT a problem of reading .po file during installation (which handles
correctly conflicts) but of business code creating new records and linked
translations (e.g. website copying website.menu records).

Removing old translations during uninstall is handled in a previous commit in
ir.model.fields _drop_column method.
This commit fixes the reinstallation on instances with leftover translations
and fixes the issue without needing a manual intervention (i.e. delete the old
translations manually).

Closes odoo/odoo#32056

Signed-off-by: Raphael Collet (rco) <rco@openerp.com>