Path getLayerFile(DescriptorDigest layerDigest, DescriptorDigest layerDiffId) {
    return getLayerDirectory(layerDigest).resolve(getLayerFilename(layerDiffId));
  }
Resolves the layer contents file.

@param layerDigest the layer digest
@param layerDiffId the layer diff Id
@return the layer contents file
jib-core/src/main/java/com/google/cloud/tools/jib/cache/CacheStorageFiles.java