Allow implicit in with lambda syntax

[ThadHouse]

Currently, if you have a delegate with an in, out, or ref parameter, you have to explicitly list all the parameter types in a lambda for that delegate. With out and ref, this makes sense and should stay that way. However, with the addition of in, I could see its use in lambdas becoming more popular (I'm using it in a new library I am creating). Since in is implicit on the calling side, if a lambda is created for a delegate with an in parameter, the in type should be allowed to be implicit. If the delegate contains both in and ref or out, then the old rules should still apply.

If a function has multiple lambda taking overloads, with one taking an in lambda, and one taking a non in lambda, the same overloads as currently with in value parameters should apply.

[alrz]

I don't like that being implicit, but rather, we could just permit the type to be omitted.

delegate void D(in int i, ref int j);

D d = (in x, ref y) => {};

[ThadHouse]

That'd be fine too. Just having to fully type out everything is a pain.

[alrz]

proposal here: #338