Type restrictions on With and WithSharedRef make generic usage of the library a little awkward

[benbelow]

For example, if I have a class Foo<T> with a property T Bar.

In v1 of the library, I could define an extension method WithBar(T myT) => builder.With(x => x.Bar, mtY), and it would work nicely.

In v4, there are type restrictions enforcing that With can only be called if T : struct, and WithSharedRef can only be called if T : class

This renders my example extension method no longer feasible, provided T is not restricted to either a struct or a class.

@Brondahl has pointed out that WithCustomSetup can be used, but it's not ideal.

Ideally we'll tweak the API such that this case is neatly supported - but in the worst case we can just call out this case in the REAMDE