Returns the (possibly negative) integer represented by the two bytes at
byteOffset in this object, in two's complement binary
The return value will be between -215 and 215 - 1, inclusive.
Throws RangeError if
byteOffset is negative, or
byteOffset + 2 is greater than the length of this object.
int getInt16(int byteOffset, [Endianness endian = Endianness.BIG_ENDIAN]);