Automatic icon loading for Spawnable doesn't work

[dmchurch]

The directions to simply place a .png in the mod directory don't work, because it looks in the wrong place, because AssetsFolder doesn't default to the mod directory.

Assembly.GetExecutingAssembly() is the wrong call here; at that instant, code from SMLHelper is running, so it will always return the SMLHelper directory.

https://github.com/SubnauticaModding/SMLHelper/blob/8dc2aae055f52cf0b9e2fdaf8a61dd768cc6bc17/SMLHelper/Assets/Spawnable.cs#L184

Leading to:

[SMLHelper/Error] Sprite for 'SurveyToolPrefab'
Did not find an image file at 'C:\Program Files (x86)\Steam\steamapps\common\Subnautica\QMods\Modding Helper\SurveyTool.png'

Presumably this wants to just reference the internal Mod field set by ModPrefab, yes?

https://github.com/SubnauticaModding/SMLHelper/blob/8dc2aae055f52cf0b9e2fdaf8a61dd768cc6bc17/SMLHelper/Assets/ModPrefab.cs#L81