Hide marker text behind planets

[HebaruSan]

Motivation

The bullseye rings are blocked by planets, but the text isn't:

Originally reported by forum user Krazy1.

Cause

The rings are LineRenderers, which exist in world space and so can be covered up by other things.

The text strings are GUI.Buttons, which are in a separate layer on top of everything else, so nothing covers them.

Ideas

Switch to UnityEngine.UI.Button and UnityEngine.UI.Text objects in world space.
So far when I try this, nothing displays, so I'm not initializing them right. Need some sample code from another mod to understand how to use them.

Also the rings should be switched from layer 9 to 31. I think the former came from TransferWindowPlanner, but stock orbit lines use the latter. This makes them disappear when you zoom out even slightly; layer 9 looks better for now.

I tried asking for help on the forum, but nobody seems to have an example of this component working in world space.