Add concatenation support and a new constructor to Godot.Collections.Array

[aaronfranke]

The primary reason for adding this is having a more consistent feature set with GDScript arrays. Test code:

var array1 = new Godot.Collections.Array("One", 2);
var array2 = new Godot.Collections.Array(3, "Four");
GD.Print(array1 + array2); // Prints [One, 2, 3, Four]

Compared to this GDScript code (there is a difference with the strings including quotation marks or not):

var array1 = ["One", 2]
var array2 = [3, "Four"]
print(array1 + array2) # Prints ["One", 2, 3, "Four"]

Test code for typed array:

var array3 = new Godot.Collections.Array<Vector2>(new Vector2(1, 2), new Vector2(3, 4));
var array4 = new Godot.Collections.Array<Vector2>(new Vector2(5, 6), new Vector2(7, 8));
GD.Print(array3 + array4); // Prints [(1, 2), (3, 4), (5, 6), (7, 8)]

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 3.2.4.