Parcel 2: ResolverRunner and default resolver

[devongovett]

This will be the object in @parcel/core which runs resolver plugins in Parcel 2. It is responsible for resolving resolver plugins from a config file and running them. Resolvers can be chained, so if one does not return anything, the next one will be called and so on.

The default resolver should be moved into @parcel/resolver-default under packages/resolvers/default, and modified to fit the new interface. Ideally this resolver could also be reused by other tools, so the interface should be easy to use and decoupled from Parcel.

[ryan-plated]

Would this fix #1813 ?

[devongovett]

Done. #2228