Fix JSON Serialization for source

[lifeiscontent]

The Type definitions say that source should be exposed, but when its transformed into JSON its not there.

[lifeiscontent]

@IvanGoncharov is it possible to backport this fix to v14?

[IvanGoncharov]

@lifeiscontent Sadly this change will make AST dumps unreadable.
Since every node will include the source.
That's why tests are falling on your PR.

[IvanGoncharov]

I need to think more about this one.
Also, it would help if someone do research on how other tools store filenames in AST.

[lifeiscontent]

@IvanGoncharov I've been working on https://github.com/lifeiscontent/storybook-addon-apollo-client

The only way I've managed to get the formatter to display code consistently is by dynamically injecting babel-plugin-graphql-tag into the storybook runtime to then parse all the code which seems to be including the source as I need (without it, the source is missing as this PR would fix) in order to display it to the user in the panel.

If you have a better suggestion on how to achieve this, please let me know.

[lifeiscontent]

Ping @IvanGoncharov