Disallow Lua activation of inventory objects

Sort of addresses #7921. It might be worthwhile to look into this further for mwscript because creating duplicate objects with the same refnum is undesirable.

Activating an object picks it up - most of the time. There's no point to activating inventory objects. If the goal is to use them, the use interface should be used instead.

At least, that's the Lua side of things. mwscript can activate inventory items and it can make sense to do so. It uses a different code path entirely though, so it's not relevant to what this MR does.