pgsql: Add more tests for EXTRACT of date type

Add more tests for EXTRACT of date type

EXTRACT of date type is implemented as a wrapper around EXTRACT of
timestamp, so the code is already tested there. But the externally
visible behavior of EXTRACT on date is not recorded anywhere. Since
there is some discussion about reimplementing or refactoring some of
this, add some more explicit tests of EXTRACT on date, similar in
structure to existing EXTRACT tests on other data types.

Discussion: https://www.postgresql.org/message-id/flat/42b73d2d-da12-ba9f-570a-420e0cce19d9(at)phystech(dot)edu

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/540612fa469eaae3345ede7a160b146dd903e7ee

Modified Files
--------------
src/test/regress/expected/date.out | 192 ++++++++++++++++++++++++++++--
src/test/regress/expected/expressions.out | 4 +-
src/test/regress/sql/date.sql | 49 +++++++-
3 files changed, 228 insertions(+), 17 deletions(-)