[IndexedDB] Consider introducing "unbounded range" (#13)

For operations like `openCursor()` that take (key or range or null) we can convert key->range but there's no range that is unbounded upper and lower that we can convert null to.

We could add:

```webidl
partial interface IDBKeyRange {
  static IDBKeyRange unbounded();
}
```

And then `openCursor(null)` is a synonym for `openCursor(IDBKeyRange.unbounded())`.


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Reply to this email directly or view it on GitHub:
https://github.com/w3c/IndexedDB/issues/13