This change allows mouse events (including enter and exit events) to
reach unfocused views on macOS. This matches the behaviour of unfocused
windows on Linux and Windows, where components paint in their "hovered"
states even when the application window is in the background.

As a byproduct of using tracking areas on macOS, we can remove the fake
mouse move generator.

When rendering with OpenGL, the paint function is called from a
background thread. If we call `isMouseOver` from the paint function, we
may end up calling native functions via the ComponentPeer, which causes
threading warnings on macOS.

This fixes warnings that are emitted when building with the `-analyze`
flag enabled.

Previously, getScreenPosition would return a result in the component's
coordinate space if it was called on a component that was not directly
or indirectly on the desktop. This behaviour is surprising and difficult
to program around. This change should ensure that the result is always
in the screen's coordinate space.