LibJS: Convert some top-level tests to the new system

First test conversions! These look really good :)

Libraries/LibJS/Tests/empty-statements.js

@@ -1,11 +1,19 @@
-try {
-    ;;;
-    if (true);
-    if (false); else if (false); else;
-    while (false);
-    do; while (false);
+test("empty semicolon statements", () => {
+    expect(";;;").toEval();
+});
 
-    console.log("PASS");
-} catch (e) {
-    console.log("FAIL: " + e);
-}
+test("if with no body", () => {
+    expect("if (true);").toEval();
+});
+
+test("chained ifs with no bodies", () => {
+    expect("if (false); else if (false); else;").toEval();
+});
+
+test("while with no body", () => {
+    expect("while (false);").toEval();
+});
+
+test("do while with no body", () => {
+    expect("do; while (false);").toEval();
+});