The CursorId class is slated for removal in 2.0, with CursorInterface::getId and Cursor::getId returning an Int64 instance. The CursorId class must be deprecated, and the tentative return types for CursorInterface::getId changed to Int64. While we could theoretically use the inheritance chain to soften the BC break, we don't consider this API to be used widely, so announcing the change and making a hard break in 2.0 is acceptable.

This will add an $asInt64 argument to Cursor::getId() to return an Int64. By default, the method will continue to return an CursorId but emit a deprecation notice when doing so.