[FR] Improvement: Change updateChildren parameter to Map<String, ?>

**Is your feature request related to a problem? Please describe.**
Various builders (e.g., `Map.of`) and language features (e.g., Groovy and Kotlin inline maps) create `Map` instances whose `V` bound is more strict than `Object`. Currently, the `DatabaseRef#updateChildren[Async]` interface won't accept these instances because it is defined as accepting `Map`.

**Describe the solution you'd like**
Since these method consume the map and do not modify it, they could be defined as `Map` to accept a map with any generic value type with no backwards incompatibility or other code changes.

**Describe alternatives you've considered**
Otherwise, passing in maps usually requires an explicit type declaration instead of `var` or an inline builder.

Cerca i punti di ingresso DatabaseRef#updateChildren e updateChildrenAsync, quindi esamina le relative dichiarazioni e tutti i test associati. Conferma che i metodi accettino Map senza modificare il comportamento di aggiornamento esistente, ed esegui la suite di test Java pertinente.

Scritto dal modello di indicizzazione a partire dal testo della issue.