Expect tests: cleanup

type:internal

Stdlib + "deduplication" made printing ASTs very annoying because of generated variables changing indexes and requiring promotions:

• moved all expect tests printing stuff (print ast-core / ast-imperative / ast-typed / mini-c) into alcotest: src/test/ast_production.ml
• prevent printing usage in src/bin/expect_tests/cli_expect.ml

side effect:

• this works: !2019 (merged)

TODO:

• typing error: do not print gen variables as such ?

Changelog details: