This is a lot nicer than the big switch full of code. This stuff has a bit
of a "please generate me instead" vibe to it, but I need to mess around with
it some more to figure out what the needs are.
This patch also unbreaks global cursor tracking, which was forgotten in the
big messaging refactoring.
In order to move the WindowServer to userspace, I have to eliminate its
dependence on system call facilities. The communication channel with each
client needs to be message-based in both directions.
Clicking the button generates a WindowCloseRequest event which the client app
then has to deal with. The default behavior for GWindow is to close() itself.
I also added a flag, GWindow::should_exit_event_loop_on_close() which does
what it sounds like it does.
This patch exposed some bugs in GWindow and GWidget teardown.
Work now happens in terms of two messages:
- WM_ClientWantsToPaint
- WM_ClientFinishedPaint
This feels fairly obvious compared to the old Paint/Invalidate.
