This implements provider inheritance during config loading, rather than
during graph evaluation. At this point it's much simpler to find the
desired configuration, and once all providers are declared, all the
inheritance code in the graph can be removed.
The inheritance is dome by simply copying the RawConfig from the parent
ProviderConfig into the module. Since this happens before any
evaluation, we record the original interpolation scope in the
ProviderConfig so that it can be properly resolved later on.
Add the Version and Providers fields to the module config.
Add ProviderConfig.Scope, which will be used to record the original
path of a ProviderConfig for interpolation.
James Bardin