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.

In cases where a VST3 plugin set a non-zero latency in its
prepareToPlay, and then set its latency to 0 later on, the host was not
notified about the latency change.

In older versions of the VST3SDK, hostContext is a raw pointer,
in newer versions it's a smart pointer. If we do manual
refcounting with the smart pointer, we may cause leaks.