feat: Add slice append (#2241)

Add slice concat

crates/nargo_cli/tests/execution_success/slices/src/main.nr

@@ -43,6 +43,11 @@ fn main(x : Field, y : pub Field) {
     assert(remove_slice[3] == 3);
     assert(remove_slice.len() == 4);
 
+    let append = [1, 2].append([3, 4, 5]);
+    assert(append.len() == 5);
+    assert(append[0] == 1);
+    assert(append[4] == 5);
+
     regression_2083();
 }
 

noir_stdlib/src/slice.nr

@@ -32,5 +32,13 @@ impl<T> [T] {
     /// the removed element
     #[builtin(slice_remove)]
     fn remove(_self: Self, _index: Field) -> (Self, T) { }
-}
 
+    // Append each element of the `other` slice to the end of `self`.
+    // This returns a new slice and leaves both input slices unchanged.
+    fn append(mut self, other: Self) -> Self {
+        for elem in other {
+            self = self.push_back(elem);
+        }
+        self
+    }
+}