pgsql: Tighten unit parsing in internal values

Tighten unit parsing in internal values

Interval values now generate an error when the user has multiple
consecutive units or a unit without a value.  Previously, it was
possible to specify multiple units consecutively which is contrary to
what the documentation allows, so it was possible to finish with
confusing interval values.

This is a follow-up of the work done in 165d581f146b.

Author: Joseph Koshakow
Reviewed-by: Jacob Champion, Gurjeet Singh, Reid Thompson
Discussion: https://postgr.es/m/CAAvxfHd-yNO+XYnUxL=GaNZ1n+eE0V-oE0+-cC1jdjdU0KS3iw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/617f9b7d4b10fec00a86802eeb34d7295c52d747

Modified Files
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src/backend/utils/adt/datetime.c       | 12 ++++++++++++
src/test/regress/expected/interval.out |  9 +++++++++
src/test/regress/sql/interval.sql      |  4 ++++
3 files changed, 25 insertions(+)