disable setinputsizes only for true DBAPI executemany
Fixed regression caused by the combination of :ticket:`8177`, re-enable
setinputsizes for SQL server unless fast_executemany + DBAPI executemany is
used for a statement, along with :ticket:`6047`, implement
"insertmanyvalues", which bypasses DBAPI executemany in place of a custom
DBAPI execute for INSERT statements. setinputsizes would incorrectly not be
used for a multiple parameter-set INSERT statement that used
"insertmanyvalues" if fast_executemany were turned on, as the check would
incorrectly assume this is a DBAPI executemany call. The "regression"
would then be that the "insertmanyvalues" statement format is apparently
slightly more sensitive to multiple rows that don't use the same types
for each row, so in such a case setinputsizes is especially needed.
The fix repairs the fast_executemany check so that it only disables
setinputsizes if true DBAPI executemany is to be used.