Fix typing of expression with inlined records

[n-osborne]

This PR proposes to improve the state of the type-checker regarding expressions involving inlined records.

This work is based on previous, not yet merged, PRs, please consider only the last 12 commits.

The PR is organised in four steps:

• the first four commits add test cases, demonstrating the behaviour we propose to improve
• the next two commits add errors, borrowed from the OCaml compiler so that error messages are closer to OCaml ones
• the next four commits refactor the encoding of symbols, proposing:
  1. to rely on types rather than on boolean encoding to distinguish between fields, functions and constructors
  2. to encode whether a constructor expect a record argument or a tuple one (inspired by how OCaml deals with inlined records)
• the penultimate commit uses the new encoding of symbols to raise the proper errors when needed and build the correct value when possible.

[n-osborne]

CI is happy. Merging.