Description of the issue/feature this PR addresses:
In pivot, when we click on '+', it must open the selection box at
the point where we click.

Current behavior before PR:
The box opens at the top of the page

Desired behavior after PR is merged:
The box opens at the point where we click

id=2066675

closes odoo/odoo#39034

X-original-commit: 989df08f
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>