input: Write a python function to create a 2D list with dimensions x by y filled with sequential numbers starting from 1.
  assert fill_2d_list(3, 5) == [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12], [13, 14, 15]]
  assert fill_2d_list(2, 3) == [[1, 2], [3, 4], [5, 6]]
  assert fill_2d_list(4, 2) == [[1, 2, 3, 4], [5, 6, 7, 8]]
output: def fill_2d_list(x, y):
      result = []
      num = 1
      for i in range(y):
          row = []
          for j in range(x):
              row.append(num)
              num += 1
          result.append(row)
      return result