Write a function `RevConcatAlternate()` that receives two slices of `int` as arguments and returns a new slice with alternated values of each slice in reverse order.
- The input slices can have different lengths.
- The new slice should contain the elements of the larger slice first and then the elements of the smaller slice.
- If the slices are of equal length, the new slice should contain the elements of the first slice first and then the elements of the second slice.
- The new slice should start with an element of the largest slice first.
- If the slices are of equal length, the new slice should start with an element of the first slice.