Bratseth/pack bits

[bratseth]

@geirst please review.

Sorry for the many commits, this was a bit exploratory.

Now that we have contextual type resolving, I want to replace the earlier half-baked attempts at type resolving by it, but this diff is already large enough.

[bratseth]

No rush, but have you seen this @geirst ?

[bratseth]

Take your time @geirst ... :-)

[bratseth]

Thanks! Yes, more work is needed on this type resolving for sure. This is just the bare minimum to support both embed and pack_bits in the same statement.