Support variadic arguments in factories

[J7mbo]

Given a factory such as:

func NewX(ys ...Y), goij tries to inject a single Y.

The Reflect package does have an IsVariadic() function in there somewhere and this can be used to detect a variadic argument.

The next step would be:

• If the type is just a struct, inject a single instance of that struct
• If the type is an interface, to find all types in the type registry that implement that interface and inject them, taking into account whether or not they are already delegated, cached, have their own factories etc.