How is the source code for multidimensional array in C# generated

For example we have a multidimensional array of doubles double[,] d = new double[1,2];

d.GetType() returns {Name = "Double[,]" FullName = "System.Double[,]"}

d[0,0] is compiled to call instance float64 float64[0..., 0...]::Get(int32, int32) IL

How is the source code of type System.Double[,] generated? Is it baked in CLR or Roslyn is responsible for its generation?