multiNamespaceInformer lack GetIndexer func

[furykerry]

Code-generator lister need an indexer to initialize, but multiNamespaceInformer does not implement GetIndexer func as sharedIndexInformer, what is the correct way to initialize a lister from multiNamespaceInformer?

lister: https://github.com/kubernetes/code-generator/blob/master/cmd/lister-gen/generators/lister.go
multiNamespaceInformer: https://github.com/kubernetes-sigs/controller-runtime/blob/main/pkg/cache/multi_namespace_cache.go