dot function
Calculates the dot product of two vec4's
@param {ReadonlyVec4} a the first operand @param {ReadonlyVec4} b the second operand @returns {Number} dot product of a and b
Implementation
List<double> dot(a, b) {
return a[0] * b[0] + a[1] * b[1] + a[2] * b[2] + a[3] * b[3];
}