"Outline" generic methods

[Ogeon]

This is mostly relevant for conversion methods that are larger than a handful of lines. It should be possible to help the compiler de-duplicate a lot of code where the same methods are used with different type parameters. Parameters such as white point or RGB standard don't affect the code more than changing a few constants, so they should be possible to "outline" as a function that is only generic over the component type:

impl<Wp: WhitePoint, T: FloatComponent> SomeType<Wp, T> {
    fn made_up_function<Wp: WhitePoint>(&self) -> Self {
        fn inner<T: FloatComponent>(a: T, b: T, c: T, white_point: (T, T, T)) -> (T, T, T) {
            // Complicated stuff...
        }

        let white_point = Wp::get_xyz().into_components();
        inner(self.a, self.b, self.c, white_point)
    }
}

This avoids generating nearly identical copies for each white point that is used. The exact way of passing the data around is up to what works best for the situation.