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.
Since applet windows live in the applet area window, the AppletManager
has to keep track of which applet is hovered and send the appropriate
enter/leave events to the applet windows.
This makes applet tooltips work again. :^)
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
