pgsql: Add date and timestamp variants of random(min, max).

Add date and timestamp variants of random(min, max).

This adds 3 new variants of the random() function:

    random(min date, max date) returns date
    random(min timestamp, max timestamp) returns timestamp
    random(min timestamptz, max timestamptz) returns timestamptz

Each returns a random value x in the range min <= x <= max.

Author: Damien Clochard <damien@dalibo.info>
Reviewed-by: Greg Sabino Mullane <htamfids@gmail.com>
Reviewed-by: Dean Rasheed <dean.a.rasheed@gmail.com>
Reviewed-by: Vik Fearing <vik@postgresfriends.org>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/f524d8cab5914613d9e624d9ce177d3d@dalibo.info

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/faf071b553830d39fc583beabcaf56ed65259acc

Modified Files
--------------
doc/src/sgml/func/func-datetime.sgml      |  30 +++++++++
doc/src/sgml/func/func-math.sgml          |   3 +-
src/backend/utils/adt/pseudorandomfuncs.c | 104 +++++++++++++++++++++++++++---
src/include/catalog/catversion.h          |   2 +-
src/include/catalog/pg_proc.dat           |  12 ++++
src/test/regress/expected/random.out      |  87 +++++++++++++++++++++++++
src/test/regress/sql/random.sql           |  26 ++++++++
7 files changed, 254 insertions(+), 10 deletions(-)