LibGUI: Ignore keydown events with Alt modifier in AbstractView

AbstractView doesn't actually do anything with them anyway, but they
would get swallowed by the cursor logic and not bubble up the widget
parent chain.

Userland/Libraries/LibGUI/AbstractView.cpp

@@ -500,6 +500,11 @@ void AbstractView::hide_event(HideEvent& event)
 
 void AbstractView::keydown_event(KeyEvent& event)
 {
+    if (event.alt()) {
+        event.ignore();
+        return;
+    }
+
     if (event.key() == KeyCode::Key_F2) {
         if (is_editable() && edit_triggers() & EditTrigger::EditKeyPressed) {
             begin_editing(cursor_index());