This is a first pass at implementing refactoring.ValidateMoves, covering
the main validation rules.
This is not yet complete. A couple situations not yet covered are
represented by commented test cases in TestValidateMoves, although that
isn't necessarily comprehensive. We'll do a further pass of filling this
out with any other subtleties before we ship this feature.
As of this commit, refactoring.ValidateMoves doesn't actually do anything
yet (always returns nil) but the goal here is to wire in the set of all
declared instances so that refactoring.ValidateMoves will then have all
of the information it needs to encapsulate our validation rules.
The actual implementation of refactoring.ValidateMoves will follow in
subsequent commits.
This is a whole lot of nothing right now, just stubbing out some control
flow that ultimately just leads to TODOs that cause it to do nothing at
all.
My intent here is to get this cross-cutting skeleton in place and thus
make it easier for us to collaborate on adding the meat to it, so that
it's more likely we can work on different parts separately and still get
a result that tessellates.
Katy Moe