Even more generalized curve API

[Multirious]

bevy_tween has built-in support for only interpolating 1D value from A to B but we should support interpolating any value from any arbitrary curve by default.

• TweenInterpolationValue(f32) should be generic or have more components. Would be changed to CurveValue<V>(V).
• Key data shouldn't be in each interpolator:
  eg. struct Translation { start: Vec3, end: Vec3 } -> struct Translation;
  Key data would be in a component like struct AtoB<V, C> { a: V, b: V }

Resulting in:

• Better foundation for 2D and 3D curves or more
• Foundation for morphing (?)