This changes the resource model to persist input and output properties
distinctly, so that when we diff changes, we only do so on the programmer-
specified input properties. This eliminates problems when the outputs
differ slightly; e.g., when the provider normalizes inputs, adds its own
values, or fails to produce new values that match the inputs.
This change simultaneously makes progress on pulumi/lumi#90, by beginning
tracking the resource objects implicated in a computed property's value.
I believe this fixes both #189 and #198.
87004a124e