This change makes progress on a few things with respect to properly
receiving properties on the engine side, coming from the provider side,
of the RPC boundary. The issues here are twofold:
1. Properties need to get unmapped using a JSON-tag-sensitive
marshaler, so that they are cased properly, etc. For that, we
have a new mapper.Unmap function (which is ultra lame -- see
pulumi/lumi#138).
2. We have the reverse problem with respect to resource IDs: on
the send side, we must translate from URNs (which the engine
knows about) and provider IDs (which the provider knows about);
similarly, then, on the receive side, we must translate from
provider IDs back into URNs.
As a result of these getting fixed, we can now properly marshal the
resulting properties back into the resource object during the plan
execution, alongside propagating and memoizing its ID.
08ca40c6c6