pgsql: Expand tests for factorial

Expand tests for factorial

Move from int4 to numeric test.  (They were originally int4 functions,
but were reimplemented for numeric in
04a4821adef38155b7920ba9eb83c4c3c29156f8.)  Add some tests for edge
cases.

Discussion: https://www.postgresql.org/message-id/flat/6ce1df0e-86a3-e544-743a-f357ff663f68%402ndquadrant.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9d402c73ade412bdeb9064c81fc4ed071c4e93f8

Modified Files
--------------
src/test/regress/expected/int4.out    | 12 ----------
src/test/regress/expected/numeric.out | 41 +++++++++++++++++++++++++++++++++++
src/test/regress/sql/int4.sql         |  4 ----
src/test/regress/sql/numeric.sql      | 11 ++++++++++
4 files changed, 52 insertions(+), 16 deletions(-)