[Err] - Map attributes should be distinct from one another on the same class

[Liamth99]

Example of code diagnostic:

// This is fine as all map attributes have a different combination of TSource and TDestination.
[Map<T, T2>]
[Map<T2, T>]
[Map<T, T3>]
public partial class Mapper;

// This is not fine as the 2 map attributes will generate the same method
[Map<T, T2>]
[Map<T, T2>]
public partial class Mapper;