Fix the optimization check to call ordinal

Fix the optimization check to call ordinal

we have some optimization to check if we can perform the string search as ordinal
operation instead of lingustic operation. we used to check if the string is Ascii
which check if all chars in the string are in range 0~7F.
This check was not enough because in Linux, ICU do some special handling for some
characters in the Ascii range. so we need to avoid calling the ordinal operation
when encountering such chracters.
The fix is to take the advantage of String.IsFastSort which do exactly what we need