Having to rely on GUI::Desktop's on_rect_change is quite limiting and a
bit awkward (continuing to use it would mean having to setup the
callback in every application using a webview) - we need a better way of
letting widgets know of a screen rect change automatically.
The specific use case will be IPWV/OOPWV which need to keep track of the
screen rect and notify the WebContent service of any change (which on
its own deliberately can't interact with WindowServer at all).
It'll also be useful for notification windows and the taskbar, which
currently both rely on the GUI::Desktop callback but will now be able to
listen and react to the event themselves.
Application.h includes Widget.h which includes Application.h. I'm not entirely
sure what the semantics are in this case, but avoiding this seems to be the
safer approach. In this case, Widget does not actually use Application, so let's
just remove the unused include.
