Mass mailing form view currently has a scrollbar for the contents of the
editor, one for the form view itself, and one for the sidebar. In
consequence we can sometimes end up with three scrollbars side by side,
which is ugly and confusing.
This ensures the height of the iframe is always that of its contents so
there is no need for a scrollbar.
When inserting a new snippet we want to autoscroll to that snippet. That
is a complicated situation because the element we want to scroll is not
in the same document as the element we want to scroll _to_.
To address that situation, a new option is added to `scrollTo` so we can
pass it the element to scroll. It can then check if we are in the
aforementioned situation, in which case it can correct the scrolling and
apply it to the right element.
We use that option in mass_mailing to prevent the bug.
Task-2545445
closes#71511
Antoine Guenet
7ed3f3151a