feat(composition): Relax @tag definition validation

[trevor-scheer]

Fixes #1021

[martijnwalraven]

I don't know if I have all the context, but implementing an immediate workaround for the lack of repeatable support in Kotlin definitely makes sense to me. I also think we want to be more lenient in allowing differences between directive definitions in general. I'd prefer if we came up with a design for that first though, and think through the consequences to make sure this is something we feel comfortable supporting for all directives.

Leaving out repeatable has no effect on the semantics of directive applications (except that there would never be more than one tag per element for that subgraph).

Additional arguments are a somewhat different case however, because we have no way of knowing what a user's intention is. So just ignoring them might be surprising or even dangerous. We may also want to differentiate between nullable and non-nullable arguments, or take default values into account.

[martijnwalraven]

Looks good to me!