New Issue: Retire 'list.extend' in favor of new 'list.append' overloads

18098, "e-kayrakli", "Retire 'list.extend' in favor of new 'list.append' overloads", "2021-07-22T23:32:31Z"

The list type has an append method that adds a new element at the end of the list. Whereas, extend is used for the same purpose but for adding more than one element (accepts lists, ranges or arrays as argument). This is based on Python's list. However, this is probably because Python has a weaker type system than Chapel's and we should be able to achieve all this by having a single method with different overloads.

This issue proposes that we deprecate/remove list.extend and add list.append overloads instead. One little hiccup there is that append returns the index at which the element is added. This may not make much sense for non-scalar appends. So, I also propose that we make append not return anything.

I don't have strong opinions beyond having a single method. append vs extend or whether append/extend returns something does not matter as much to me.