[FIX] website, *: always allow scroll for popup taller than window

*: web_editor

Steps to reproduce:
- Activate the cookie dialog from the website settings
- Remove the backdrop from the cookie dialog
- Add some blocks to the cookie dialog in the website editor
until the dialog height is bigger than the page height.

Result:
The cookie dialog is not scrollable, so it's impossible to reach
the "I agree" button and close the dialog, leaving the user stuck
at the first page.

I check if the popup content is higher than the window. If it is, I
give priority to the popup scroll over the page one. I had to
overwrite the _showElement method to call _setScrollbar after
the content rendering, in this way I can get its correct height.
I also try to update the scrollbar each time a block in the cookie bar
has been changed and each time the window resize. This is optimize, so
if the overflow isn't changed from the last time I tried to update the
scrollbar no action will be taken. In this way you can always see the
whole popup without refreshing the page.

Also I have to set 'pointer-events' to none only if the popup is
smaller than the page itself (to interact with and scroll the
page behind), otherwise the popup won't be scrollable. I did
this by adding a class "s_popup_overflow_page" if the popup is
higher than the page and I adapted the pointer-events
property accordingly.

opw-2660786

closes odoo/odoo#80092

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