pgsql: Fixes for multirange selectivity estimation

Fixes for multirange selectivity estimation

 * Fix enumeration of the multirange operators in calc_multirangesel() and
   calc_multirangesel() switches.
 * Add more regression tests for matching to empty ranges/multiranges.

Reported-by: Alexander Lakhin
Discussion: https://postgr.es/m/c5269c65-f967-77c5-ff7c-15e621c47f6a%40gmail.com
Author: Alexander Korotkov
Backpatch-through: 14, where multiranges were introduced

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/322e82b77ef4acb9697c6e4259292f5671cb85bb

Modified Files
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src/backend/utils/adt/multirangetypes_selfuncs.c |  38 ++--
src/test/regress/expected/multirangetypes.out    | 210 +++++++++++++++++++++++
src/test/regress/sql/multirangetypes.sql         |  37 ++++
3 files changed, 272 insertions(+), 13 deletions(-)