Consume OldInputs when diffing in infer

[iwahbe]

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Issue details

infer currently assumes that old inputs will be included in resource outputs when diffing. At the time, that was the best it could do but we now have access to the OldInputs field on gRPC. We should use that when available.

Affected area/feature

pulumi-go-provider/infer/resource.go

Lines 964 to 977 in 80e4b89

	inputProps, err := introspect.FindProperties(new(I))
	if err != nil {
	return p.DiffResponse{}, err
	}
	// Olds is an Output, but news is an Input. Output should be a superset of Input,
	// so we need to filter out fields that are in Output but not Input.
	oldInputs := resource.PropertyMap{}
	for k := range inputProps {
	key := resource.PropertyKey(k)
	oldInputs[key] = req.Olds[key]
	}
	objDiff := oldInputs.Diff(req.News)
	pluginDiff := plugin.NewDetailedDiffFromObjectDiff(objDiff, false)
	diff := map[string]p.PropertyDiff{}