[FIX] slides: prevent the # anchors of the PDF controllers from triggering a scroll jump

PURPOSE

Currently, the PDF viewer is loaded from an iframe and the PDF controllers
contains empty anchor links. When the user clicks on one of these links,
the browsers based on Chromium will trigger a "scroll jump" and the iframe
will be placed at the top of the browser window.

When the PDF document is larger than the viewport, this behavior can be
quite annoying: The user will have to scroll the browser window to
see the controllers each time they click on a controller (-> link) as
(1) the controllers triggers a scroll jump and (2) the controllers are
below the document that does not fit entirely on screen. To avoid that,
we will add an event listener that returns false on each controller. The
controllers will then no longer trigger a scroll jump.

SPECS

- Add an event listener on the PDF controllers links to prevent a scroll jump.

LINKS

Task id: 2500574

closes odoo/odoo#73816

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>