[Solid/Core] Support modifying empty query data

[kyjus25]

It is currently only possible to edit the query data (in this case, an array of items) if it already has data. If my endpoint returns an empty array, or worse - nothing, I would like the ability to add an item to the array for testing.

Given that this is not already possible and seems explicitly disabled I worry there may be a technical reason (though possible programmatically with setQueryData), but would like to open the discussion.

Loading (Pending)	Success (Empty Array)	Success (Populated Array)