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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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/bdee4af8e07648008fe522fc5a562db453be5ad7

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(-)