pgsql: Add get_opfamily_name() function

Add get_opfamily_name() function

This refactors and simplifies various existing code to make use of the
new function.

Reviewed-by: Mark Dilger <mark(dot)dilger(at)enterprisedb(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/E72EAA49-354D-4C2E-8EB9-255197F55330(at)enterprisedb(dot)com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/43493cceda2fb75e07a63cec46000407661d505d

Modified Files
--------------
contrib/bloom/blvalidate.c | 12 ++----------
src/backend/access/brin/brin_validate.c | 12 ++----------
src/backend/access/gin/ginvalidate.c | 12 ++----------
src/backend/access/gist/gistvalidate.c | 11 +----------
src/backend/access/hash/hashvalidate.c | 11 +----------
src/backend/access/nbtree/nbtvalidate.c | 11 +----------
src/backend/access/spgist/spgvalidate.c | 11 +----------
src/backend/commands/indexcmds.c | 30 ++----------------------------
src/backend/utils/cache/lsyscache.c | 27 +++++++++++++++++++++++++++
src/include/utils/lsyscache.h | 1 +
10 files changed, 40 insertions(+), 98 deletions(-)