Implement int32x4.GetX, GetY, GetZ and GetW, float32x4.withX, withY,
withZ and withW, int32x4.withX, withY, withZ and withW,
int32x4.withFlagX, int32x4.withFlagY, int32x4.withFlagZ and
int32x4.withFlagW
Handle MIRType_Boolean in inlining and type conversion