LibJS: Rewrite Parser.parse_object_expression()

This rewrite drastically increases the accuracy of object literals.
Additionally, an "assertIsSyntaxError" function has been added to
test-common.js to assist in testing syntax errors.

Libraries/LibJS/Tests/test-common.js

@@ -50,6 +50,18 @@ function assertThrowsError(testFunction, options) {
     }
 }
 
+/**
+ * Ensures the provided JavaScript source code results in a SyntaxError
+ * @param {string} source The JavaScript source code to compile
+ */
+function assertIsSyntaxError(source) {
+    assertThrowsError(() => {
+        new Function(source)();
+    }, {
+        error: SyntaxError,
+    });
+}
+
 /**
  * Ensures the provided arrays contain exactly the same items.
  * @param {Array} a First array