[no squash] Improve building into spot dug same cycle

[j-r]

NOTE: this PR also includes two mostly unrelated changes, because they touch the same code, but I'll remove the second change if requested

Digging and building in the same cycle doesn't remove the dug node, but directly tries to place the new node. Unfortunately when the new node requires its custom on_place to be called this will often not work, because that on_place will typically check for the target position to be air or buildable_to which for a node dug in the same cycle mostly won't be the case.

There doesn't seem to be an issue for that, but it is easily reproduced using default:torch:

• build a digtron with a builder directly behind a digger (i.e. both targeting the same position in a cycle)
• configure the builder to place torches on the ground
• run the digtron on flat ground and note that it places torches on the ground
• place a stone in front of the digger, and start the digtron seeing that it removes the stone, but fails to place the torch (and a warning from core.item_place_node is logged)

This PR fixes this by explicitly removing the dug node before invoking on_place of the new node.

Now that the code knows whether it builds into a spot dug the same cycle, this PR also introduces a small, but neat feature: allow extrusion to be zero, meaning to only build, if the target position was dug the same cycle. This e.g. allows to use soft material digger to detect an unstable roof and have the builder seal it using stone, but not build a roof if there is air above (e.g. in a large cave). This change is really small, so I included it here, but I can submit it separately (if the fix is merged).

[j-r]

Hopefully improved the comment. It is still a bit longer than your suggestion, because a reminder that the dug node isn't removed yet would have helped me back then.