Improve the manipulation of nested data structures

[AllergicMushroom]

I think the current manipulation tools for nested data structures could be improved. As mentionned in #2611, I think a cell could contain another table, accessible via the enter input. Consider the following jsonl example.

{ "A": { "NA": 1, "NB": 2 }, "B": 100 }

The cell (1, "A") contains the nested table { "NA": 1, "NB": 2 }.
Placing the cursor in this cell and pressing enter should give access to the underlying table.

However, there is still a question of how to display the nested data structure when we are viewing the main table.