[IMP] web_editor: ease drag and drop understanding

Ease the understanding of the drag'n drop of a snippet. Users test have
demonstrated that one doesn't understand how to add a snippet on the page.

* Rotate the snippet once clicked, as it is for tasks in project application.
* Keep the position of the mouse.

task-2261817

closes odoo/odoo#51905

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>