bloom: Optimize bitmap scan path with streaming read

bloom: Optimize bitmap scan path with streaming read

This commit replaces the per-page buffer read look in blgetbitmap() with
a reading stream, to improve scan efficiency, particularly useful for
large bloom indexes.  Some benchmarking with a large number of rows has
shown a very nice improvement in terms of runtime and IO read reduction
with test cases up to 10M rows for a bloom index scan.

For the io_uring method, The author has reported a 3x in runtime with
io_uring while I was at close to a 7x.  For the worker method with 3
workers, the author has reported better numbers than myself in runtime,
with the reduction in IO stats being appealing for all the cases
measured.

Author: Xuneng Zhou <xunengzhou@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Nazir Bilal Yavuz <byavuz81@gmail.com>
Discussion: https://postgr.es/m/CABPTF7VrqfbcDXqGrdLQ2xaQ=K0RzExNuw6U_GGqzSJu32wfdQ@mail.gmail.com