Add test for maximal nesting of arrays/objects

[nlohmann]

Almost all JSON parsers have limitations in the maximal nesting of arrays or objects. While

[[[[[[[[[[[[[[[[[[[["Too deep"]]]]]]]]]]]]]]]]]]]]

certainly will break no library any more, having the same input with a few thousand more [] will. It would be great to know the limits of the libraries.

[Loki-Astari]

I don't see much real value in this.
It's more of an implementation oddity on who can support the deepest nested array structure. In real life I would not expect to see 20 level nested array (or anything like that). IF you can support 20 levels you will be able to support any real life json objects that you find in the wild.

[nlohmann]

I disagree that there is no value in it, because it is also a security issue if you can crash your parser with just a few bytes yielding a stack overflow.

[Loki-Astari]

OK. I sort of agree with that.