Mark an annotation as the one under the pointer, or null for none. Views that show the same
annotations (the grid's tags, a host's list) read RangeAnnotationState.hovered so that
pointing at one lights the other. A pointer leaving should pass the id it entered with through
unhoverRangeAnnotation, so a leave that arrives after the next enter does not clear it.
Mark an annotation as the one under the pointer, or
nullfor none. Views that show the same annotations (the grid's tags, a host's list) read RangeAnnotationState.hovered so that pointing at one lights the other. A pointer leaving should pass the id it entered with through unhoverRangeAnnotation, so a leave that arrives after the next enter does not clear it.