pgsql: Allow negative aggtransspace to indicate unbounded state size

Allow negative aggtransspace to indicate unbounded state size

This patch reuses the existing aggtransspace in pg_aggregate to
signal that an aggregate's transition state can grow unboundedly.  If
aggtransspace is set to a negative value, it now indicates that the
transition state may consume unpredictable or large amounts of memory,
such as in aggregates like array_agg or string_agg that accumulate
input rows.

This information can be used by the planner to avoid applying
memory-sensitive optimizations (e.g., eager aggregation) when there is
a risk of excessive memory usage during partial aggregation.

Bump catalog version.

Per idea from Robert Haas, though applied differently than originally
suggested.

Discussion: https://postgr.es/m/CA+TgmoYbkvYwLa+1vOP7RDY7kO2=A7rppoPusoRXe44VDOGBPg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/185e304263347d0979832f7a08a812872d136b18

Modified Files
--------------
doc/src/sgml/catalogs.sgml               |  5 ++++-
doc/src/sgml/ref/create_aggregate.sgml   | 11 ++++++++---
src/include/catalog/catversion.h         |  2 +-
src/include/catalog/pg_aggregate.dat     | 10 ++++++----
src/test/regress/expected/opr_sanity.out |  2 +-
src/test/regress/sql/opr_sanity.sql      |  2 +-
6 files changed, 21 insertions(+), 11 deletions(-)