Use strtoi64() in pgbench, replacing its open-coded implementation

Use strtoi64() in pgbench, replacing its open-coded implementation

Makes the code a little simpler.

The old implementation accepted trailing whitespace, but that was
unnecessary. Firstly, its sibling function for parsing decimals,
strtodouble(), does not accept trailing whitespace. Secondly, none of
the callers can pass a string with trailing whitespace to it.

In the passing, check specifically for ERANGE before printing the "out
of range" error. On some systems, strtoul() and strtod() return EINVAL
on an empty or all-spaces string, and "invalid input syntax" is more
appropriate for that than "out of range". For the existing
strtodouble() function this is purely academical because it's never
called with errorOK==false, but let's be tidy. (Perhaps we should
remove the dead codepaths altogether, but I'll leave that for another
day.)

Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Yuefei Shi <shiyuefei1004@gmail.com>
Reviewed-by: Neil Chen <carpenter.nail.cz@gmail.com>
Discussion: https://www.postgresql.org/message-id/861dd5bd-f2c9-4ff5-8aa0-f82bdb75ec1f@iki.fi