Support lazy query execution

[mesarth]

Implement https://jg-rp.github.io/json-p3/quick-start#lazy-queries

Research:

• Does lazy query make the use of separate threads for query execution obsolete, because the CancellationToken can be checked regularly while iterating over the result? Does this allow the extension to be used in the web?

[mesarth]

Looked into this a bit.

We still have to use a seperate thread for query execution because the controller is apparently run on the UI thread (becomes unresponsive).

Regardless of that, it would have been nice to stream the result nodes to the cell output as soon as they become available. The main problem seems to be that our result is always a JSON array, which has to be added at once. Therefore we have to replace the complete result array after each iteration which is not performant.