List; add remove(value)

Having to encode this behaviour at every call site is tedious. It makes a lot of sense to just have the method available on list itself.

test/core/list/remove.wren

@@ -0,0 +1,18 @@
+var a = [1, 2, 3]
+a.remove(2)
+System.print(a) // expect: [1, 3]
+
+var b = [1, 2, 3]
+b.remove(1)
+System.print(b) // expect: [2, 3]
+
+var c = [1, 2, 3]
+c.remove(3)
+System.print(c) // expect: [1, 2]
+
+// Return the removed value.
+System.print([3, 4, 5].remove(4)) // expect: 4
+System.print([3, 4, 5].remove(5)) // expect: 5
+
+// Return null when not found
+System.print([1, 2, 3].remove(8)) // expect: null