feat: `queryCursorAsStream`

https://github.com/ReactiveX/rxdart/pull/696

```dart
Stream queryCursorAsStream(
String table, {
bool? distinct,
List? columns,
String? where,
List? whereArgs,
String? groupBy,
String? having,
String? orderBy,
int? limit,
int? offset,
int? bufferSize,
}) =>
Rx.using(
() => queryCursor(
table,
distinct: distinct,
columns: columns,
where: where,
whereArgs: whereArgs,
groupBy: groupBy,
having: having,
orderBy: orderBy,
limit: limit,
offset: offset,
bufferSize: bufferSize,
),
(cursor) async* {
while (await cursor.moveNext()) {
yield cursor.current;
}
},
(cursor) => cursor.close(),
);
```