When marshaling a resource reference as its ID (i.e. when
opts.KeepResources is false, as it will be in the case of downlevel SDKs
and resource providers), we must take care to marshal/unmarshal an empty
ID as the unknown property value.
This includes the following changes to the resource ref APIs:
- Bifurcate resource reference creation into two methods: one for
creating references to custom resources and one for creating
references to component resources.
- Store the ID in a resource reference as a PropertyValue s.t. it can be
computed.
- Add a helper method for retrieving the ID as a string + an indicator of
whether or not the reference has an ID.
Fixes#5939.
2f0dba23ab