WL#4068: Improve INSERT DELAYED component to increase query throughput

INSERT DELAYED component suffers from a few design flaws which could be
addressed by easily copy known patterns. There is no reason why a INSERT DELAYED
should be slower than a batched INSERT.

Suggestions:

1) Improve producer-consumer pattern by introducing spin-buffers. This will
scale better with many insert threads.
2) Improve handler throughput by writing data with handler::bulk_insert(). This
will make the consumer thread work much more efficiently as we loop over much
smaller instruction sets and also allows us to take advantage of any SE specific
optimization.