Rename #[cgp_dispatch] to #[cgp_auto_dispatch]

[soareschen]

Summary

This PR renames the upcoming #[cgp_dispatch] macro to #[cgp_auto_dispatch].

This is to reserve the original name #[cgp_dispatch] so that it can be applied on CGP traits. On the other hand, #[cgp_auto_dispatch] is designed as a simplfied tool to work with regular enums, so that users don't need to adopt the full CGP to use it.

Example

#[cgp_auto_dispatch] will be used for cases like:

#[cgp_auto_dispatch]
pub trait HasArea {
    fn area(&self) -> f64;
}

On the other hand, in the future a new #[cgp_dispatch] will be implemented for CGP traits like:

#[cgp_dispatch]
#[cgp_component(AreaComputer)]
pub trait CanComputeArea<Shape> {
    fn compute_area(&self, shape: &Shape) -> f64;
}

where the dispatching is done on Shape instead of Self.