Preserve overlays when users pause tours / anchor overlays in world space, not screen space

[pkgw]

Consider a tour with graphical overlays like the S&T New Year's Eve Stars tour.

If you're playing it back and pause the tour, the overlays fade away. One likely reason for this behavior is that the overlays are positioned in screen space, not world space, so that if you were to keep showing them, they'd stay anchored on screen as the user navigates around the sky. Not a great experience in the common case that overlays are labeling something on the sky.
It would be nice to preserve the overlays, which would require finding a way to anchor them in the world coordinate frame rather than the screen coordinate frame. This is extra-tricky if you start considering 3D mode.

One semi-hacky approach might be to convert the overlays into Annotations when the tour is paused, at least to the extent possible — annotations are anchored to the sky.

CC @astrodavid10