Use native JSON in Elixir

[TylerWitt]

What are you trying to accomplish?

This removes the only dependency used for Elixir in processing the Hex ecosystem.

It should remove some dependency management from maintaining Hex, as it's all within Elixir's standard library now.

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.

[abdulapopoola]

Thanks @TylerWitt , looking forward to your contribution!

[TylerWitt]

Stalled on elixir-lang/elixir#14193