`naga::valid::ConstantError::UnresolvedComponent` and `UnresolvedSize` are no longer necessary

[Jim Blandy]

Now that handles are validated separately before carrying out any other validation, there should be no need for the validator to ever return naga::valid::ConstantError::UnresolvedComponent or UnresolvedSize. These should be removed.

cc @ErichDonGubler

[Erich Gubler]

I have been successfully nerd sniped. 😆