LibWebView+WebContent: Propagate unconsumed input events out of OOPWV

Since 9e2bd9d261a8c0c1b5eeafde95ca310efc667204, the OOPWV has been
consuming all mouse and keyboard events, preventing action shortcuts
from working. So let's fix that. :^)

OOPWV now queues up input events, sending them one at a time to the
WebContent process and waiting for the new
`did_finish_handling_input_event(bool event_was_accepted) =|` IPC call
before sending the next one. If the event was not accepted, OOPWV
imitates the usual event bubbling: first passing the event to its
superclass, then to its parent widget, and finally propagating to any
Action shortcuts.

With this, shortcuts like Ctrl+I to open Browser's JS console work
again, except when a contenteditable field is selected. That's a
whole separate stack of yaks.

Co-authored-by: Zaggy1024 <zaggy1024@gmail.com>

Userland/Services/WebContent/ConnectionFromClient.h

@@ -98,6 +98,8 @@ private:
 
     void flush_pending_paint_requests();
 
+    void report_finished_handling_input_event(bool event_was_handled);
+
     NonnullOwnPtr<PageHost> m_page_host;
     struct PaintRequest {
         Gfx::IntRect content_rect;