This "upgrades" various nsLayoutUtils functions which take as inputs
a set of coordinates and a frame that the coordinates are relative to,
to accept a RelativeTo object instead of a frame.

Most of the patch is just dumb propagation, but the few places where
we use an explicit ViewportType::Visual are important. There are
probably a few other places I've overlooked, but this seems to cover
the important ones that come up commonly.

There are undoubtedly other functions into which we can propagate
RelativeTo, in this patch I've propagated it as far as necessary
for my needs in this bug (mainly GetTransformToAncestor() and
GetEventCoordinatesRelativeTo()).

Differential Revision: https://phabricator.services.mozilla.com/D68919