Add Land Mine trigger range visualization

[HeliGungir]

TL;DR: When placing or hovering a Land Mine, show a circle that visualizes their (or its) trigger area, similar to turrets.

Their trigger and damage radius are not the same. Trigger radius is 2.5 tiles, damage radius is 3.0 tiles.

I believe the trigger area is the most important thing to visualize. (I only know the trigger radius because of the wiki, and first discovered they were different when a killbox I designed did not trigger Land Mines as expected.)

Since Land Mines can be spammed a lot, performance of the visualization might be an issue. If it is an issue, an acceptable compromise would be to only show the range of one Land Mine: The one in your cursor, or the one your cursor is hovering over.