Returns an array containing all the members of a supplied array, plus one additional member at the end.
array:append( $array as array(*),$appendage as item()*array(*)The result is an array whose size is array:size($array) + 1, in which all
members in positions 1 to array:size($array) are the same as the members in the corresponding position
of $array, and the member in position array:size($array) + 1 is $appendage.
The result is equivalent to the result of the expression
op:array-concat( $array, [$appendage] ).
The expression array:append(["a", "b", "c"], "d") returns ["a", "b", "c", "d"].
The expression array:append(["a", "b", "c"], ("d", "e")) returns ["a", "b", "c", ("d", "e")].
The expression array:append(["a", "b", "c"], ["d", "e"]) returns ["a", "b", "c", ["d", "e"]].
