pgsql: Use streaming I/O in ANALYZE.

Use streaming I/O in ANALYZE.

The ANALYZE command prefetches and reads sample blocks chosen by a
BlockSampler algorithm. Instead of calling [Prefetch|Read]Buffer() for
each block, ANALYZE now uses the streaming API introduced in b5a9b18cd0.

Author: Nazir Bilal Yavuz <byavuz81@gmail.com>
Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Jakub Wartak <jakub.wartak@enterprisedb.com>
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://postgr.es/m/flat/CAN55FZ0UhXqk9v3y-zW_fp4-WCp43V8y0A72xPmLkOM%2B6M%2BmJg%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/041b96802efa33d2bc9456f2ad946976b92b5ae1

Modified Files
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src/backend/access/heap/heapam_handler.c | 29 ++++++-----
src/backend/commands/analyze.c           | 85 ++++++++++----------------------
src/include/access/heapam.h              |  5 +-
3 files changed, 43 insertions(+), 76 deletions(-)