Implement `Database` interface on iOS

[westnordost]

Requires #5412.

Implement the Database.kt interface for iOS using libsqlite3, analogous to android-specific implementation in AndroidDatabase

Currently, the code that creates the database file if it does not exist yet and opens the database in a thread-safe way is done StreetCompleteSQLiteOpenHelper (that inherits functionality from the Android class SQLiteOpenHelper. This functionality either needs to be reimplemented in platform-independent code or be reimplemented on iOS side.

[westnordost]

Note: https://developer.android.com/kotlin/multiplatform/sqlite is a multiplatform sqlite library, which may remove the necessity to implement Database on iOS separately.

It is multiplatform-capable since v2.5.0, which has been in alpha since May 2014 (as of 2025-01-08, it is at alpha 12)

(Not blocked anymore because this could be implemented right away, without the need to setup the project as multiplatform)