pgsql: Introduce XLogRecPtrIsValid()

Introduce XLogRecPtrIsValid()

XLogRecPtrIsInvalid() is inconsistent with the affirmative form of
macros used for other datatypes, and leads to awkward double negatives
in a few places. This commit introduces XLogRecPtrIsValid(), which
allows code to be written more naturally.

This patch only adds the new macro. XLogRecPtrIsInvalid() is left in
place, and all existing callers remain untouched. This means all
supported branches can accept hypothetical bug fixes that use the new
macro, and at the same time any code that compiled with the original
formulation will continue to silently compile just fine.

Author: Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>
Backpatch-through: 13
Discussion: https://postgr.es/m/aQB7EvGqrbZXrMlg@ip-10-97-1-34.eu-west-3.compute.internal

Branch
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REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/c0031d461324ca6063e96cc28ce78b75aa778112

Modified Files
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src/include/access/xlogdefs.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)