LibJS: Add function call spreading

Adds support for the following syntax:

    myFunction(...x, ...[1, 2, 3], ...o.foo, ...'abcd')

Libraries/LibJS/Tests/function-spread.js

@@ -0,0 +1,27 @@
+load("test-common.js");
+
+try {
+    const sum = (a, b, c) => a + b + c;
+    const a = [1, 2, 3];
+
+    assert(sum(...a) === 6);
+    assert(sum(1, ...a) === 4);
+    assert(sum(...a, 10) === 6);
+
+    const foo = (a, b, c) => c;
+
+    const o = { bar: [1, 2, 3] };
+    assert(foo(...o.bar) === 3);
+    assert(foo(..."abc") === "c");
+
+    assertThrowsError(() => {
+        [...1];
+    }, {
+        error: TypeError,
+        message: "1 is not iterable",
+    });
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}