Structured diagnostics for the compiler

[Octachron]

See also ocaml/RFCs#45 and https://icfp24.sigplan.org/details/ocaml-2024-papers/16/Structured-diagnostics-for-the-OCaml-compiler for previous discussions .

A limitation of the current compiler diagnostics (error messages, warnings, time profile information and other compiler developer debugging output) is that it cannot be parsed easily and reliably by developer tools. This creates an impedance mismatch between the compiler and those tools that tend to resort to trying to parse manually compiler error message.

This PR proposes to fix this problem by adding to the compiler a machinery for building structured compiler diagnostics before displaying them in various formats.

This PR is probably best reviewed commit by commit:

• the first eight commits slowly introduce the new machinery part by part
• commit 9 to 14 converts the current compiler diagnostics to this new machinery (going through the error messages, the debugging outputs, then the toplevel, and finally the compiler configuration)
• commit 15 adds a new tools for instrospecting the compiler diagnostics, and the following commit uses this new tools
  to export json-schema and adds the corresponding tests in the testsuite
• the last commits 4 commits update the manual and the man pages.

[Octachron]

Note that I have tested some quick prototypes for deserializers and a bridge between the proposed compiler diagnostic and the grace library at https://github.com/Octachron/sdiag-prototypes .

[johnyob]

Note that I have tested some quick prototypes for deserializers and a bridge between the proposed compiler diagnostic and the grace library at https://github.com/Octachron/sdiag-prototypes .

Its lovely to see grace being used here :) I look forward to playing with this