refactor: Replace TS-based with string-based preprocessed introspection output

[kitten]

Follow-up to #150
Follow-up to #152

Summary

This removes the TypeScript-based introspection outputs in favour of string-based introspection type outputs.

The problem with the former is, while the code will be useful for outputting types later on, for introspections it's simply too slow to run in GraphQLSP.

Set of changes

• Put introspection code into internal/src/introspection
• Rewrite introspection output with string-based logic
• Add tests

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Latest commit: fdfc2ae

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