Check for intersection between placed blocks and entities. (#3850)

* Check for intersection between placed blocks and entities.

+ Implemented GetPlacementCollisionBox, to permit custom placement collision boxes for blocks.

* Factored block-entity placement checking into another function in cPlayer.

- Removed vector min/max functions

* Use GetWorld to get the world in DoesPlacingBlocksIntersectEntity.

+ Added block height checks, allow different cEntity subclasses to decide whether they will prevent block placement.

Server/Plugins/APIDump/APIDesc.lua

@@ -3059,6 +3059,16 @@ local Hash = cCryptoHash.sha1HexString("DataToHash")
 					},
 					Notes = "Schedules the entity to be destroyed; if ShouldBroadcast is not present or set to true, broadcasts the DestroyEntity packet",
 				},
+				DoesPreventBlockPlacement =
+				{
+					Returns =
+					{
+						{
+							Type = "boolean",
+						},
+					},
+					Notes = "Returns true if this entity doesn't allow blocks to be placed intersecting the entity.",
+				},
 				GetAirLevel =
 				{
 					Returns =