pgsql: Allow sibling call optimization in slot_getsomeattrs_int()

Allow sibling call optimization in slot_getsomeattrs_int()

This changes the TupleTableSlotOps contract to make it so the
getsomeattrs() function is in charge of calling
slot_getmissingattrs().

Since this removes all code from slot_getsomeattrs_int() aside from the
getsomeattrs() call itself, we may as well adjust slot_getsomeattrs() so
that it calls getsomeattrs() directly. We leave slot_getsomeattrs_int()
intact as this is still called from the JIT code.

Author: David Rowley <dgrowleyml(at)gmail(dot)com>
Reviewed-by: Andres Freund <andres(at)anarazel(dot)de>
Reviewed-by: Zsolt Parragi <zsolt(dot)parragi(at)percona(dot)com>
Discussion: https://postgr.es/m/CAApHDvodSVBj3ypOYbYUCJX%2BNWL%3DVZs63RNBQ_FxB_F%2B6QXF-A%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4deecb52affa4b6f791e8a57f6584610e4dd12f4

Modified Files
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src/backend/executor/execTuples.c | 58 ++++++++++++++++++++-------------------
src/include/executor/tuptable.h | 13 +++++----
2 files changed, 38 insertions(+), 33 deletions(-)