IMPALA-4023: don't attach buffered tuple streams to batches
This simplifies the memory transfer model by eliminating one category of
resources that can be attached.
This patch also separates the concepts of attaching resources and
flushing resources. Previously RowBatch::AddTupleStream() implicitly
flushed resources from the ExecNode pipeline, which various ExecNodes
relied on to free up memory reservations for subsequent processing. In a
subsequent patch I want the FlushResources() API to become stronger: it
will force streaming ExecNodes to flush their batches or forces
blocking ExecNodes to acquire ownership of the memory resources.
We can't do this right now since we don't have a way to transfer
ownership of BufferedBlockMgr Blocks.
Reviewed-by: Tim Armstrong <firstname.lastname@example.org>
Tested-by: Internal Jenkins