Allow scaffolding to create collapsable ceilings

Normally Sand, Gravel, Red Sand, etc. in ceilings will generate floating, and it's impossible to put them back because they will always obey gravity.

But what if we could use a Scaffolding pillar to fix that?

The idea is for Sand, Gravel, Red Sand, Snow, etc to be 'stuck' when placed on top of a Scaffolding block, as long as there is at least one other solid block adjacent to them (on the side or directly above).

Then when the Scaffolding is collapsed, the gravity-obeying block stays put.

This shouldn't apply to Anvils or Dragon Eggs, obviously. But the other blocks that generate naturally in suspension should be able to be 'fixed' in this way.