pgsql: docs: improve AT TIME ZONE description - Mailing list pgsql-committers

docs:  improve AT TIME ZONE description

The previous description was unclear.  Also add a third example, change
use of time zone acronyms to more verbose descriptions, and add a
mention that using 'time' with AT TIME ZONE uses the current time zone
rules.

Backpatch-through: 9.3

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/838fd62cab520a5ae15fdab30d0f962070571bdb

Modified Files
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doc/src/sgml/func.sgml | 32 +++++++++++++++++++++-----------
1 file changed, 21 insertions(+), 11 deletions(-)