2.9.1.3.4.4 DataView.prototype.GetInt16(byteOffset, littleEndian)
Gets the Int16 value at offset byteOffset in the DataView, using the provided endianness.
Let O be ToObject(this)
Let isLittleEndian be ToBoolean(littleEndian) if provided, else false
If the [[Class]] internal property of O is not "DataView", raise a TypeError.
Return GetValue(byteOffset, isLittleEndian, Int16)