pgsql: Change fastgetattr and heap_getattr to inline functions

Change fastgetattr and heap_getattr to inline functions

They were macros previously, but recent callsite additions made Coverity
complain about one of the assertions being always true. This change
could have been made a long time ago, but the Coverity complain broke
the inertia.

Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Reviewed-by: Japin Li <japinli(at)hotmail(dot)com>
Reviewed-by: Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com>
Discussion: https://postgr.es/m/202203241021.uts52sczx3al@alvherre.pgsql

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e27f4ee0a701854daf16ac1d044f20d28a17053e

Modified Files
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src/backend/access/heap/heapam.c | 46 ------------
src/include/access/htup_details.h | 151 +++++++++++++++++---------------------
2 files changed, 69 insertions(+), 128 deletions(-)