The expanded bounding box as [west, south, east, north], or null if the visible area is too small
Use it when you want a specific geographic area (toBeContainedBBox) fully visible in the unobscured
portion of the map (the area UI components don't cover). The function returns a larger bounding
box that accounts for the space the UI elements take.
It expands the latitudes in Web Mercator, as fitBounds frames them, and they stay within its ±85.051129.
The returned longitudes can pass ±180, as fitBounds takes them: east always does for a
toBeContainedBBox across the antimeridian, with west greater than east, and either one does when
the expansion reaches past it.
Calculates an expanded bounding box that, when the map zooms to it, keeps the given to-be-contained bounding box visible within the area surrounding UI elements don't obscure, optional padding included.