[FW][FIX] web: allow drag and drop elements in mass_mailing

[fw-bot]

Issue:

We can't move elements in mass mailing.

Steps to reproduce the issue:

• Create a new mass mailing with a template that have some blocks
• Try to drag one of the blocks to another position
• When you click on the button to drag, the right sidebar refreches

Origin of the issue:

The issue was first introduced by 1.

The problem when we have the wysiwyg inside an iframe document.activeElement will be equal to the iframe element and the ev.target is the button of dragging. In reality the button is inside the iframe but the content of the iframe is like this <iframe> document <iframe> so contains returns false.

Solution:

When the activeElement is an iframe we search inside its contentDocument.

opw-4196067

Forward-Port-Of: odoo/odoo#181143

[robodoo]

[fw-bot]

This PR targets saas-17.2 and is part of the forward-port chain. Further PRs will be created up to master.

More info at https://github.com/odoo/odoo/wiki/Mergebot#forward-port