State buggy on track mouseover

[zepumph]

copied from phet-io repo https://github.com/phetsims/phet-io/issues/965

@samreid said:

See https://github.com/phetsims/phet-io/issues/533

When dragging (but not yet dropping) a control point over another track, there is an intermediate glitch. @zepumph and I decided this doesn't need to be fixed for customization, since it is unlikely that the user will have their mouse dragging a control point when a state is saved, but if the state save/load was reused for accessibility interviews (or other reasons for state playback), this would be problematic.

[marlitas]

I can't tell from this description if this is a fix we would want to include in the upcoming publication. It doesn't sound critical to phet-io performance, but I'm also not sure if state playback is a feature that is being used right now. @kathy-phet what are your thoughts here?

[marlitas]

PhET-iO brand is not part of the upcoming region and culture publication. Marking as deferred.