Write a method called rectSum that will get the sum of a rectangle of elements within a 2D array of ints
with corners (r0,c0) and (r1,c1), inclusive (that is, include element (r0,c0) and (r1,c1). (Hint: use a
nested loop)
public static int rectSum(int[][] s, int r0, int c0, int r1, int c1)