Opening Mimic inventory needs improvement

Mimics can still move while inventory is open, which can cause some unintended issues with it suddenly closing (think Chest Minecarts that travel too far from a player while opened). Some client/server sync for players accessing a Mimic should be implemented (Chests do this, reference that for examples).

Additionally, this can help to provide a way to add in the open/close animation for Mimics when accessing inventory.