Entity selector: don't remove selected entities from the full list

[sophiamersmann]

• We've had user feedback that it's annoying that a selected entity moves to the "Selection" section at the top since this makes quickly selecting/unselecting an entity cumbersome
• The animation is also suboptimal in other cases. For example, we're not currently automatically closing the entity selector modal since that looks broken because the animation gets interrupted.
• Marwa suggested keeping a full list of all entities always, i.e. if a new entity is selected, it does appear in the "Selection" section on top, but it doesn't disappear from the full list