Dragon eggs, scaffolding, anvils, and pointed dripstone drop as items while falling through cobwebs

Relates to MC-170802 and MC-2085.

The bug

While falling through a cobweb, dragon eggs, scaffolding, and anvils drop as items, even if there is space below the cobweb for them to land. This also affects sand, gravel, and concrete powder, but those are covered in the related tickets.

How to reproduce

1. Place a cobweb with an air block below it.
2. If testing dragon eggs or anvils, place a block above the cobweb and then place the egg or anvil above the block. If testing scaffolding, build a small scaffolding tower and then bridge out until the scaffolding is no longer supported and falls.
3. If testing dragon eggs or anvils, break the block that it is resting on.
4. Wait.