LibJS: Add Array.prototype.splice

Adds splice to Array.prototype according to the specification:
https://tc39.es/ecma262/#sec-array.prototype.splice

Libraries/LibJS/Tests/Array.prototype-generic-functions.js

@@ -27,6 +27,18 @@ try {
         assert(o.length === 0);
     });
 
+    {
+        const o = { length: 3, 0: "hello", 2: "serenity" };
+        const removed = Array.prototype.splice.call(o, 0, 2, "hello", "friends");
+        assert(o.length === 3);
+        assert(o[0] === "hello");
+        assert(o[1] === "friends");
+        assert(o[2] === "serenity");
+        assert(removed.length === 2);
+        assert(removed[0] === "hello");
+        assert(removed[1] === undefined);
+    }
+
     {
         assert(Array.prototype.join.call({}) === "");
         assert(Array.prototype.join.call({ length: "foo" }) === "");

Libraries/LibJS/Tests/Array.prototype.splice.js

@@ -0,0 +1,87 @@
+load("test-common.js");
+
+try {
+    assert(Array.prototype.splice.length === 2);
+
+    var array = ["hello", "friends", "serenity", 1, 2];
+    var removed = array.splice(3);
+    assert(array.length === 3);
+    assert(array[0] === "hello");
+    assert(array[1] === "friends");
+    assert(array[2] === "serenity");
+    assert(removed.length === 2);
+    assert(removed[0] === 1);
+    assert(removed[1] === 2);
+
+    array = ["hello", "friends", "serenity", 1, 2];
+    removed = array.splice(-2);
+    assert(array.length === 3);
+    assert(array[0] === "hello");
+    assert(array[1] === "friends");
+    assert(array[2] === "serenity");
+    assert(removed.length === 2);
+    assert(removed[0] === 1);
+    assert(removed[1] === 2);
+
+    array = ["hello", "friends", "serenity", 1, 2];
+    removed = array.splice(-2, 1);
+    assert(array.length === 4);
+    assert(array[0] === "hello");
+    assert(array[1] === "friends");
+    assert(array[2] === "serenity");
+    assert(array[3] === 2);
+    assert(removed.length === 1);
+    assert(removed[0] === 1);
+
+    array = ["serenity"];
+    removed = array.splice(0, 0, "hello", "friends");
+    assert(array.length === 3);
+    assert(array[0] === "hello");
+    assert(array[1] === "friends");
+    assert(array[2] === "serenity");
+    assert(removed.length === 0);
+
+    array = ["goodbye", "friends", "serenity"];
+    removed = array.splice(0, 1, "hello");
+    assert(array.length === 3);
+    assert(array[0] === "hello");
+    assert(array[1] === "friends");
+    assert(array[2] === "serenity");
+    assert(removed.length === 1);
+    assert(removed[0] === "goodbye");
+
+    array = ["foo", "bar", "baz"];
+    removed = array.splice();
+    assert(array.length === 3);
+    assert(array[0] === "foo");
+    assert(array[1] === "bar");
+    assert(array[2] === "baz");
+    assert(removed.length === 0);
+
+    removed = array.splice(0, 123);
+    assert(array.length === 0);
+    assert(removed.length === 3);
+    assert(removed[0] === "foo");
+    assert(removed[1] === "bar");
+    assert(removed[2] === "baz");
+
+    array = ["foo", "bar", "baz"];
+    removed = array.splice(123, 123);
+    assert(array.length === 3);
+    assert(array[0] === "foo");
+    assert(array[1] === "bar");
+    assert(array[2] === "baz");
+    assert(removed.length === 0);
+
+    array = ["foo", "bar", "baz"];
+    removed = array.splice(-123, 123);
+    assert(array.length === 0);
+    assert(removed.length === 3);
+    assert(removed[0] === "foo");
+    assert(removed[1] === "bar");
+    assert(removed[2] === "baz");
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}