Add exceptions when using a non-requested submodule

[Reinms]

Many submodules currently fail silently when they are not requested, this can lead to confusion for developers if they happen to forget a submodule dependency attribute.

In addition, logging a simple error is not always sufficient because it is not always immediately apparent that the error is due to something on their end.

This change should be non breaking for all mods that don't rely on the (not defined) behaviour of an unrequested submodule.

[Reinms]

Also adds a very simple helper method to LoadoutAPI which allows the following syntax:

//Old:
mySkill.activationState = new SerializableEntityStateType(typeof(MySkillState));
//New:
mySkill.activationState = LoadoutAPI.StateTypeOf<MySkillState>();
//New:
using static R2API.LoadoutAPI;
mySkill.activationState = StateTypeOf<MySkillState>();