2022-9: An Average Window (or a Windowed Average)

Write code that:

- takes a second argument Y that is a numeric scalar or non-empty vector.

- takes a first argument X that represents the number of neighboring elements on either side of each element in Y.

- returns a numeric vector or scalar where each element is the average (mean) of the corresponding element in Y and its X neighbors on either side. If an element has fewer than X neighbors on either side, replicate the first and last values as necessary to make X neighbors.