Remove unused class
Remove uses of IterableTransformer
Add separate deterministic flag to SHOW FUNCTIONS
Fix SHOW FUNCTIONS test
Add documentation to Operator interface
Add default implementation of Operator.isBlocked
Make Operator implement AutoCloseable
Do not call finish on operators if the task is already failed or canceled
Replace QueryExecution.cancel with fail(USER_CANCELED)
Split stage cancel and abort
Split task cancel and abort