pgsql: Don't use is_infinite() where isinf() will do.

Don't use is_infinite() where isinf() will do.

Places that aren't testing for sign should not use the more expensive
function; it's just wasteful, not to mention being a cognitive load
for readers who may know what isinf() is but not is_infinite().

As things stand, we actually don't need is_infinite() anyplace except
float4out/float8out, which means it could potentially go away altogether
after the changes I proposed in <13178.1538794717@sss.pgh.pa.us>.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0209f0285d9b1c60bf74cc9f5f0133d7bdd887c3

Modified Files
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src/backend/utils/adt/formatting.c          |  4 ++--
src/backend/utils/adt/rangetypes_selfuncs.c | 14 ++++++++------
2 files changed, 10 insertions(+), 8 deletions(-)