pgsql: Add local_blk_{read|write}_time I/O timing statistics for local

Add local_blk_{read|write}_time I/O timing statistics for local blocks

There was no I/O timing statistics for counting read and write timings
on local blocks, contrary to the counterparts for temp and shared
blocks.  This information is available when track_io_timing is enabled.

The output of EXPLAIN is updated to show this information.  An update of
pg_stat_statements is planned next.

Author: Nazir Bilal Yavuz
Reviewed-by: Robert Haas, Melanie Plageman
Discussion: https://postgr.es/m/CAN55FZ19Ss279mZuqGbuUNxka0iPbLgYuOQXqAKewrjNrp27VA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/295c36c0c1fa7b6befd0a3525c7f109e838c9448

Modified Files
--------------
doc/src/sgml/ref/explain.sgml          |  4 ++--
src/backend/commands/explain.c         | 23 ++++++++++++++++++++++-
src/backend/executor/instrument.c      |  6 ++++++
src/backend/utils/activity/pgstat_io.c |  4 ++++
src/include/executor/instrument.h      |  2 ++
src/test/regress/expected/explain.out  |  4 ++++
6 files changed, 40 insertions(+), 3 deletions(-)