Feature request: ability to get the path of JsonVariant in a document

[gwisp2]

Hello! Thanks for the great library!

I suggest adding ability to get the path of JsonVariant in a document, or at least to check that two JsonVariant point to the same location of the document. The latter can be used to implement the former by traversing the whole document. As I understand JsonVariant::operator==() compares content, not pointers.

My usecase: I parse some JSON structures received from network and if parsing fails I would like to easily send back error messages with the exact path to json part that caused a parsing error.