*: web, web_editor

Since the right-panelization made with [1], the modals were not
compensating the body scrollbar when opened anymore and the backdrop
was misplaced. This commit fixes the problems generically, to support
modals with non-body scrolling.

[1]: https://github.com/odoo/odoo/pull/57975

closes odoo/odoo#58414

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

*: web, web_editor, portal, account, website_blog, website_forum

This is probably not ideal to move the scrolling behavior out of the
html element but this will be needed for the editor to not have a double
scrollbar on the right. This is actually also useful for the scrollbar
to appear under the purple odoo menu instead of its right.

This commit, if to be reverted in the future, however contains many
improvements to make the transition easier that should be kept: jQuery
and Odoo functions to be able to scrollTo a specific element, get the
top scrollable element, check if an element is scrollable, etc. Also,
some magic was done: if some code tries to scroll to a specific scroll
position via jQuery's scrollTop or animate functions on the html/body
element, those will still work as intended (obviously, using the new
utils to do that is however recommended).

This commit also reviews our scroll behaviors to make them more robust
and share the code.

Part of https://github.com/odoo/odoo/pull/57975
task-2344227

*: web

Part of https://github.com/odoo/odoo/pull/49142
task-2229551

Co-authored-by: qsm-odoo <qsm@odoo.com>

This commit moves the flex rules of #wrapwrap div to web so it can be used in
survey.

This is needed to make the survey footer stick to the bottom of the screen
even if main has not enough content to fill the page.

This commit prepares survey redesign.

Task ID: '2150291'
PR #43237