This fixes an issue in Live 11.2 where editors using OpenGL would be
scaled incorrectly after closing and reopening the editor.

On Windows, the OpenGL context window sometimes receives a repaint
request after moving between screens with different scale factors.
If the screen has changed size/scale since the last paint operation,
failing to invalidate the painted area may cause the screen contents
to be drawn at the wrong scale until paint is next called.

This patch also makes Optional public to end users.

This includes Carbon support

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