pgsql: Add test coverage for EXTRACT()

Add test coverage for EXTRACT()

The variants for time and timetz had zero test coverage, the variant
for interval only very little. This adds practically full coverage
for those functions.

Reviewed-by: Vik Fearing <vik(at)postgresfriends(dot)org>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://www.postgresql.org/message-id/flat/c3306ac7-fcae-a1b8-1e30-6a379d605bcb%402ndquadrant.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/378badc8ebebc8fece7a18001f6b876cc00b12c0

Modified Files
--------------
src/test/regress/expected/date.out | 25 ----------
src/test/regress/expected/interval.out | 84 ++++++++++++++++++++++++++++++++++
src/test/regress/expected/time.out | 45 ++++++++++++++++++
src/test/regress/expected/timetz.out | 61 ++++++++++++++++++++++++
src/test/regress/sql/date.sql | 5 --
src/test/regress/sql/interval.sql | 32 +++++++++++++
src/test/regress/sql/time.sql | 13 ++++++
src/test/regress/sql/timetz.sql | 15 ++++++
8 files changed, 250 insertions(+), 30 deletions(-)