Ensure forward build compatibility for resource provider

[AaronFriel]

See: pulumi/pulumi#11616

This change ensures the Docker provider is source-code forward compatible with future changes to the gRPC interfaces for providers upstream. This reduces the likelihood that source code changes are needed when updating to new Pulumi SDK/PKG versions.

The same change is being made in the bridge and other providers to ensure that CI systems can reliably build and test new versions of the core Pulumi engine against providers.

[github-actions]

Does the PR have any schema changes?

Looking good! No breaking changes found.
No new resources/functions.

[guineveresaenger]

Could you please provide a top-level summary in this pull request? You linked to a p/p change, where you describe the problem being addressed, but could you describe the solution as well, and also any implications for this provider?

Do we need to add anything like this to the terraform bridge?

[AaronFriel]

@guineveresaenger I've added some context, but the tracking issue should be the "source of truth", IMO. Otherwise we'll end up duplicating a lot of information across different threads. The tracking issue has a PR against the bridge, which is already merged.

The implication for this provider is that it avoids the following error message, which you would see if you updated to the latest pulumi/pulumi/sdk/v3:

./serve.go:33:9: cannot use &dockerHybridProvider{…} (value of type *dockerHybridProvider) as type pulumirpc.ResourceProviderServer in return statement:
        *dockerHybridProvider does not implement pulumirpc.ResourceProviderServer (missing GetMapping method)
./serve.go:37:20: cannot use nativeProvider (variable of type *dockerNativeProvider) as type pulumirpc.ResourceProviderServer in struct literal:
        *dockerNativeProvider does not implement pulumirpc.ResourceProviderServer (missing GetMapping method)

By embedding the UnimplementedResourceProviderServer type in dockerHybridProvider and dockerNativeProvider, those types gain default implementations of the GetMapping method.

[guineveresaenger]

Thank you!!