As explained in pulumi/pulumi-fabric#293, we were a little ad-hoc in
how configuration was "applied" to resource providers.
In fact, config wasn't ever communicated directly to providers; instead,
the resource providers would simply ask the engine to read random heap
locations (via tokens). Now that we're on a plan where configuration gets
handed to the program at startup, and that's that, and where generally
speaking resource providers never communicate directly with the language
runtime, we need to take a different approach.
As such, the resource provider interface now offers a Configure RPC
method that the resource planning engine will invoke at the right
times with the right subset of configuration variables filtered to
just that provider's package. This fixespulumi/pulumi#293.
This refactors the engine so all of the APIs on it are instance
methods on the type instead of raw methods that float around and use
data from a global engine.
A mechcanical change as we remove the global `E` and then make
anything that interacted with that in pkg/engine to be an instance
method and the dealing with the fallout.
Instead of talking directly to stdout or stderr via methods on fmt,
indirect through an Engine type (presently a global, but soon to
change) to allow control of where the streams actually end up.
