transforming every vec2 into vec2<float> and GenericVec2<T> into vec2<T>

[Duskhorn]

This is a paired effort alongside project-imprimis/libprimis-headers#14 to make a common vec2<T> struct for the whole engine.

There still exists the ivec struct which has deliberately left untouched for the time being, even though one could "theoretically" exchange it with vec2<int>