Converts the given number to a signed 16-bit integer (`int16`) by rounding to the nearest whole number and typecasting.
If the number exceeds the range of an `int16` (-32,768 to 32,767), it will wrap due to typecasting.
s16(value)
s16(12345.6); // returns 12346
s16(-40000); // returns 25536 (wrap)
s16(70000); // returns 4464 (wrap)