Piglin brutes should drop chest keys

The brutes were added to make the bastions harder, but instead of just being harder to kill they should serve more perpose. They should drop keys to a new type of chest that replaces the current bastion chests (perhaps a blackstone tomb-like container). Without the key, these chests take much longer to break and have a chance of only dropping some of the loot. If you use a key, the key has a chance of breaking so it can't be used to open other Blackstone chests. this will greatly improve the complexity and challenge of raiding a bastion by adding a new form of risk and reward in gathering loot. :)