pgsql: Invent random_normal() to provide normally-distributed random nu

Invent random_normal() to provide normally-distributed random numbers.

There is already a version of this in contrib/tablefunc, but it
seems sufficiently widely useful to justify having it in core.

Paul Ramsey

Discussion: https://postgr.es/m/CACowWR0DqHAvOKUCNxTrASFkWsDLqKMd6WiXvVvaWg4pV1BMnQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/38d81760c4d7e22b95252e3545596602c9e38806

Modified Files
--------------
doc/src/sgml/func.sgml | 26 ++++++++++++++++++++-
src/backend/catalog/system_functions.sql | 7 ++++++
src/backend/utils/adt/float.c | 40 ++++++++++++++++++++++++++++----
src/bin/pgbench/pgbench.c | 24 +++----------------
src/common/pg_prng.c | 37 ++++++++++++++++++++++++++++-
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_proc.dat | 4 ++++
src/include/common/pg_prng.h | 1 +
src/test/regress/expected/random.out | 28 ++++++++++++++++++++++
src/test/regress/sql/random.sql | 24 +++++++++++++++++++
10 files changed, 164 insertions(+), 29 deletions(-)