LibJS+LibWeb: Log JavaScript exceptions raised by web content

Instead of hiding JS exceptions raised on the web, we now print them to
the debug log. This will make it a bit easier to work out why some web
pages aren't working right. :^)

Libraries/LibWeb/DOM/Document.cpp

@@ -488,8 +488,10 @@ Color Document::visited_link_color() const
 static JS::VM& main_thread_vm()
 {
     static RefPtr<JS::VM> vm;
-    if (!vm)
+    if (!vm) {
         vm = JS::VM::create();
+        vm->set_should_log_exceptions(true);
+    }
     return *vm;
 }