pgsql: Provide fast path in snprintf.c for conversion specs that areju

Provide fast path in snprintf.c for conversion specs that are just "%s".

This case occurs often enough (around 45% of conversion specs executed
in our regression tests are just "%s") that it's worth an extra test
per conversion spec to allow skipping all the logic associated with
field widths and padding when it happens.

Discussion: https://postgr.es/m/26193.1538582367@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6d842be6c11887930a0f4128fd6aa4de427cfd2a

Modified Files
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src/port/snprintf.c | 13 +++++++++++++
1 file changed, 13 insertions(+)