Add NightVisionEquipmentPrototype::brightness_to_turn_on

[snouz]

Hi, I'm humbly asking for the opposite setting to darkness_to_turn_on for NightVision Equipment.

MY USE CASE
Making sunglasses for my sun-adjacent planet, Moshine. I would like to add some times in the day where the light makes it impossible to see clearly, which would be resolved by having these sun-goggles. This would greatly add to the ambiance of the planet.

[boskid]

I will consider this implemented in 2.1.21.

Modding:
- Added NightVisionEquipmentPrototype::sunglasses.