SelectNext: cap listbox's max height to available space

[acelaya]

SelectNext implements some logic that makes the listbox drop up or down depending on where there's more available space.

However, the max height is "hardcoded" (via tailwind class), which means it can partially render out of the viewport.

It would be good to calculate not only where there's more space (in order to decide if it should drop up or down), but also check the available space, and set a max height which is slightly smaller.