Logic for checking isImageSharable

[Shubhranshu153]

Running command:
nerdctl build . --platform vs docker build . --platform has a different behaviour
With nerdctl it falls back to type docker/oci which leads it to export a tar file and then loading the image, this has a significant performance impact.

Checking the logic of:

executor == "containerd" && containerdUUID == uuid && containerdNamespace == namespace && workerSnapshotter == snapshotter && len(platform) == 0, nil

is it possible this is mapping too many conditional for is-shareable? This is creating some unintended behavior and delays due to tar creation

Logic in docker for setting exporter type to "image"

switch len(opt.Exports) {
	case 1:
		// valid
	case 0:
		if nodeDriver.IsMobyDriver() && !noDefaultLoad() {
			// backwards compat for docker driver only:
			// this ensures the build results in a docker image.
			opt.Exports = []client.ExportEntry{{Type: "image", Attrs: map[string]string{}}}
		}
	default:
		return nil, nil, errors.Errorf("multiple outputs currently unsupported")
	}

Thank You