template literalize

[sakari]

Remove dependency to typescript AST. The typescript AST is not very stable API and causes us to have to change oats for new ts versions. Instead we now generate the code using template strings. A bit less type safety but a lot less prone to breaking with ts versions.

This should not change the behaviour or the semantics of the generated code -- just generation and possibly whitespace. Note that the integration tests in /test have not been changed.

This pr also refactors type generation code to be more testable

For one major user of the code generation the resulting code is the same modulo newlines and trailing commas and handling of incorrectly defined objects schemas. That and all the integration tests passing give some confidence that the generation works.

todo

• use string literals for generating types
• release canary and create some test builds in projects using oats to see if tests pass in actual use

[sakari]

we use prettier internally to print typescript code

[lautis]

Agree with the reasoning – at least currently the AST approach has been a bit flaky and would expect even more changes with TypeScript 7. Having prettier 2 as runtime dependency is a bit annoying, but as discussed in Slack, we can fix that relatively easily.