Player->useHeldItem() assumes that if the old item == the new item, we want to set the item back into the inventory if it's modified in-place. Therefore, we don't modify the item in-place to bypass the problem.
closes#4022
this action (which is more accurately referred to as 'activate item' or 'use item' in other areas) always fires on right-click when holding any item, whether aiming at a block or not.
in pretty much every case, these usages really wanted to read the tag's contents anyway, which can be combined with a getTag() and instanceof call for more concise and static analysis friendly code.
In the few cases where the tag contents wasn't needed, it still wanted to check the type, which, again, can be done in a more static analysis friendly way by just using getTag() and instanceof.
