Make IR vision behave like real IR vision

**Is your feature request related to a problem? Please describe.**
Currently IR vision items and mutations are some kind of heat camera thing that can see through walls. This doesn't make sense.

**Describe the solution you'd like**
IR vision should allow you to see infrared light. Seeing through walls should go. This would add an interesting layer to visibility as it would allow for things like IR lasers and IR flashlights to be visible to the player without being visible to monsters without IR vision. IR vision for monsters and robots would be a feature for them.

Start by locating the handling for IR vision items and mutations, then trace the visibility behavior that currently permits seeing through walls. Define how infrared light should be represented for players, monsters, and robots, and verify that IR lasers and flashlights are visible only to entities with IR vision.

Written by the indexing model from the issue text.