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.

This new factoring is a bit more typesafe, as it avoids casting
internals to void*.

It also allows cursors to scale appropriately on high resolution
displays on Windows.

Hosts such as REAPER normalise the program parameter value by dividing
the program value by the step count, rather than going via the
parameter's toNormalized function. To be compatible, we should use the
same scaling technique. At time of writing, the coversion process is
detailed under the heading "Conversion of normalized values" on this
page:

https://developer.steinberg.help/display/VST/Parameters+and+Automation

This change is designed to fix issues with views stealing focus and
being brought to the front when popup menus are dismissed.

To test this behaviour:
- Open two instances "a" and "b" of a plugin editor containing a
  ComboBox
- Click the ComboBox in editor "a", opening its PopupMenu
- Drag the titlebar of editor "b" to move it
- The PopupMenu should be dismissed, but editor "a" should *not* steal
  keyboard focus or be brought to the front

Previously, Xcode's main thread checker would complain when selecting
the "OpenGL Renderer" in the DemoRunner on macOS.

Fixes a bug introduced in 7d1918b385c600e1910dd5b744b583a42a26d8a1,
where Ozone 9's editor failed to open correctly in the AudioPluginHost.

The issue was caused by DropShadower using the ComponentListener interface
to listen to its target Component's changes and creating shadow Components
only if the target was visible during the event callbacks. However it was
possible that during the events the target was not yet visible because one
of its parents was not visible. When the parent became visible it would not
trigger a callback for the observed child component.

The fix attaches a ComponentListener recursively to all parents starting
from the target and responds to each componentVisibilityChanged() event.