pgsql: Fix EXPLAIN ANALYZE for parallel HashAgg plans

Fix EXPLAIN ANALYZE for parallel HashAgg plans

Since 1f39bce02, HashAgg nodes have had the ability to spill to disk when
memory consumption exceeds work_mem. That commit added new properties to
EXPLAIN ANALYZE to show the maximum memory usage and disk usage, however,
it didn't quite go as far as showing that information for parallel
workers.  Since workers may have experienced something very different from
the main process, we should show this information per worker, as is done
in Sort.

Reviewed-by: Justin Pryzby
Reviewed-by: Jeff Davis
Discussion: https://postgr.es/m/CAApHDvpEKbfZa18mM1TD7qV6PG+w97pwCWq5tVD0dX7e11gRJw@mail.gmail.com
Backpatch-through: 13, where the hashagg spilling code was added.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9bdb300dedf086cc54edf740088208e6b24307ef

Modified Files
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src/backend/commands/explain.c      | 110 +++++++++++++++++++++++++++++++-----
src/backend/executor/execParallel.c |  19 ++++++-
src/backend/executor/nodeAgg.c      | 103 +++++++++++++++++++++++++++++++++
src/include/executor/nodeAgg.h      |   7 +++
src/include/nodes/execnodes.h       |  22 ++++++++
5 files changed, 244 insertions(+), 17 deletions(-)