Allow transparent divs to be considered "top layers"

This changes the meaning of `was_top_layer` so that it is checking that
nothing opaque is on top of the given layer. The layer in question
need not be opaque.
2979eb9da9Max Brunsfeld committed on 12/19/2023, 2:32:08 AMparentb88370d
1 file changedLine totals unavailable