pgsql: Fix extract epoch from interval calculation

Fix extract epoch from interval calculation

The new numeric code for extract epoch from interval accidentally
truncated the DAYS_PER_YEAR value to an integer, leading to results
that mismatched the floating-point interval_part calculations.

The commit a2da77cdb4661826482ebf2ddba1f953bc74afe4 that introduced
this actually contains the regression test change that this reverts.
I suppose this was missed at the time.

Reported-by: Joseph Koshakow <koshy44(at)gmail(dot)com>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://www.postgresql.org/message-id/flat/CAAvxfHd5n%3D13NYA2q_tUq%3D3%3DSuWU-CufmTf-Ozj%3DfrEgt7pXwQ%40mail.gmail.com

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/7a8d8219ccbf0963f2171ea23e1616ee6a7823ba

Modified Files
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src/backend/utils/adt/timestamp.c | 14 ++++++++++----
src/test/regress/expected/interval.out | 4 ++--
2 files changed, 12 insertions(+), 6 deletions(-)