[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.

搜尋 DatabaseRef#updateChildren 和 updateChildrenAsync 進入點，然後檢查它們的宣告及任何相關測試。確認這些方法接受 Map，且不變更其現有的更新行為，並執行相關的 Java 測試套件。

由索引模型根據 Issue 內容生成。