Resolver implementation use of unsafe code is not sound

[yamadapc]

Resolver has the following unsafe pieces of code:

• Lifetimes casts due to use of Arenas for String interning
• Mutable string cast to remove JSON comments from JSON string

This is not sound & likely causes undefined behaviour on certain cases.

It's likely unnecessary:

• We can parse JSON into an owned structure that isn't borrowing from the input
• We can use a JSON5 parser to handle comments and trailing commas

[yamadapc]

We have started to observe regular segmentation faults around this code in production.

[yamadapc]

This now is critical as it is reported daily by multiple developers.

It will start to be fixed by - #9885