Add a way to know the current "init" status of the FS

The FS should be able to tell what is the current name with which it was initialized the last time (And maybe the options). Right now the only way to know the name is by querying `fsInstance.promises._backend._store` and check if it is undefined or if it has a `_storeName` this would be useful to not initialize the same database twice when you have multiple databases in the same thread that depend on user options