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_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/723cc84db50a7b822f89c3ea90cbd39d530d1f70

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