LibWeb: Require parent window argument for MessageBox

Since the vast majority of message boxes should be modal, require
the parent window to be passed in, which can be nullptr for the
rare case that they don't. By it being the first argument, the
default arguments also don't need to be explicitly stated in most
cases, and it encourages passing in a parent window handle.

Fix up several message boxes that should have been modal.

DevTools/HackStudio/TerminalWrapper.cpp

@@ -44,12 +44,10 @@
 void TerminalWrapper::run_command(const String& command)
 {
     if (m_pid != -1) {
-        GUI::MessageBox::show(
+        GUI::MessageBox::show(window(),
             "A command is already running in this TerminalWrapper",
             "Can't run command",
-            GUI::MessageBox::Type::Error,
-            GUI::MessageBox::InputType::OK,
-            window());
+            GUI::MessageBox::Type::Error);
         return;
     }