makeResourceRawConfig hides unschematized fields

[t0yv0]

This is a subtle change in behavior from DiffStrategy=Classic to DiffStrategy=PlanState uncovered by the test suite when
testing PlanState in the following PR:

#1976

The failing tests highlight a change in how un-schematized fields are exposed to the provider in RawConfig during Read.
Before the change, the user program could have a property set in the inputs that is not present in the schema, and this
property would get inflected into a Pulumi naming convention and get exposed in RawConfig.

It is peculiar that this would happen with an implicit warning:

pulumi-terraform-bridge/pkg/tfshim/sdk-v2/cty.go

Line 57 in 98847bf

return makeResourceRawConfigClassic(config, resource)

makeResourceRawConfigClassic would swallow an error from CoerceValue stating:

    unexpected attribute "raw_config_value"

And then would continue recovering raw config on the approximate path:

    // Once more, choosing to proceed with a slightly incorrect value rather than fail fast.
    glog.V(9).Infof("failed to coerce config: %v", err)
    return original

Assuming this functionality is very rarely relied on, but if it was needed, we should consider implementing this
differently to avoid triggering the panic in CoerceValue, first splitting the data into schematized and un-schematized
parts, then calling CoerceValue on the schematized parts, and then joining the translated unschematized parts back.

[VenelinMartinov]

Have we observed any providers relying on this behaviour?

[t0yv0]

Haven't observed this yet being relied on in the actually user-facing providers, just in the test suite.