Decide whether resources/corpses should have an obstruction, and if so how and which.

[wraitii]

This ticket follow #3530 and [17156]

In [17156] I made it so that entities that become resources upon death (chicken...) get a passable (it does not block anything) static obstruction. This fixes a bug and makes the behavior saner.

We should decide how to generalize this behavior: should some entities get a blocking obstruction? How do we decide the size of this obstruction?

Do we want this behavior for corpses too? If so it could go in decay.

[elexis]

• Player-created animals like sheep should not block, as the user could block siege with a ton of dead sheep
• Whale, sharks, fish and other sea animals should not block, no matter if alive or dead IMO
• I wouldn't mind other corpses block, especially elephants

Notice it is important to assign the correct radius to the different corpse types, otherwise units won't be gathering at the correct place.

[elexis]

As mentioned in #3530, gatherable corpses are only one case where obstructions with clearance 0 can occur, there might be other cases we don't know about yet.

That's why we should still add the warning and ignore obstructions with clearance zero, i.e. attachment:t3530_throw_warnings.patch:ticket:3530​ and attachment:testLine.patch:ticket:3530​