Improve Plist and JSON Encoder/Decoder resilience to errors thrown during coding

[zintus]

_JSONDecoder internal state could be corrupted by trying to decode failing nested object. Fix this by ensuring storage stack pop after error throw.

Resolves SR-6408.

[itaiferber]

Thanks for putting this together! SR-6408 is related to SR-6078 — I've been meaning to put together the comprehensive fixes here but have not yet had the time. If we're going to fix this, do you mind please also addressing SR-6078 and applying these fixes to PropertyListEncoder/PropertyListDecoder as well?

Also, we'd want to introduce unit tests to ensure that this does what we think it does, and doesn't regress in the future.

[zintus]

Now SR-6078 should be fixed too.

I didn't invest much time in setting up build/test environment, should work on it more

[CodaFi]

Looks like this was covered by #13879. If I'm wrong about that, please reopen this and rebase it to fix the merge conflicts.

[zintus]

Should be fixed by #13879, thanks for looking at it.