compiler packages for the OCaml 5.3.0~beta1

[Octachron]

This PR adds three packages for the first beta release of OCaml 5.3.0:

• the usual ocaml-base--compiler and ocaml-variants packages
• the newish ocaml-compiler package

Compared to the first alpha, this beta includes 3 runtime fixes, 2 type system fix and a handful numbers of fixes for the runtime event library. This beta also adds a new -keywords compatibility flag in order to help compiling old code that are using the new keyword effect as a standard identifier.

---

Changes compared to the first alpha:

Runtime bug fixes

• (13502): Fix misindexing related to Gc.finalise_last that could prevent
  finalisers from being run.
  (Nick Roberts, review by Mark Shinwell)

• (13402), (13512), (13549), (13553): Revise bytecode implementation of callbacks
  so that it no longer produces dangling registered bytecode fragments.
  (Xavier Leroy, report by Jan Midtgaard, analysis by Stephen Dolan,
  review by Miod Vallat)

• (13520): Fix compilation of native-code version of systhreads. Bytecode fields
  were being included in the thread descriptors.
  (David Allsopp, review by Sébastien Hinderer and Miod Vallat)

Type system bug fixes

• (13579), (13583): Unsoundness involving non-injective types + gadts
  (Jacques Garrigue, report by @v-gb,
  review by Richard Eisenberg and Florian Angeletti)

• (13388), (13540): raises an error message (and not an internal compiler error)
  when two local substitutions are incompatible (for instance module type S:=sig end type t:=(module S))
  (Florian Angeletti, report by Nailen Matschke, review by Gabriel Scherer, and
  Leo White)

Compiler CLI

• (13471): add -keywords <version?+list> flag to define the list of keywords
  recognized by the lexer, for instance -keywords 5.2 disable the effect
  keyword.
  (Florian Angeletti, review by Gabriel Scherer)

Runtime event library fixes

• (13419): Fix memory bugs in runtime events system.
  (B. Szilvasy and Nick Barnes, review by Miod Vallat, Nick Barnes,
  Tim McGilchrist, and Gabriel Scherer)

• (13407): Add Runtime_events.EV_EMPTY_MINOR
  (Thomas Leonard)

• (13522): Confirm runtime events ring is still active after callback.
  (KC Sivaramakrishnan, review by Sadiq Jaffer and Miod Vallat)

• (13529): Do not write to event ring after going out of stw participant set.
  (KC Sivaramakrishnan, review by Sadiq Jaffer)

Documentation

• (13424): Fix Gc.quick_stat documentation to clarify that returned fields
  live_words, live_blocks, free_words, and fragments are not zero.
  (Jan Midtgaard, review by Damien Doligez and KC Sivaramakrishnan)

• (13440): Update documentation of Gc.{control,get,set} to reflect fields
  not currently supported on OCaml 5.
  (Jan Midtgaard, review by Gabriel Scherer)

• (13469), (13474), (13535): Document that [Hashtbl.create n] creates a hash table
  with a default minimal size, even if [n] is very small or negative.
  (Antonin Décimo, Nick Bares, report by Nikolaus Huber and Jan Midtgaard,
  review by Florian Angeletti, Anil Madhavapeddy, Gabriel Scherer,
  and Miod Vallat)

Standard library internal fix

• (13543): Remove some String-Bytes conversion from the stdlib to behave better
  with js_of_ocaml
  (Hugo Heuzard, review by Gabriel Scherer)

Toplevel bug fix

• (13263), (13560): fix printing true and false in toplevel and error
  messages (no more unexpected #true)
  (Florian Angeletti, report by Samuel Vivien, review by Gabriel Scherer)

Compiler internals

• (13391), (13551): fix a printing bug with -dsource when using
  raw literal inside a locally abstract type constraint
  (i.e. let f: type \#for. ... )
  (Florian Angeletti, report by Nick Roberts, review by Richard Eisenberg)

[shonfeder]

The only CI error is

Warning in ocaml-compiler.5.3.0~beta1: The package has a dune-project file but no explicit dependency on dune was found.

And I suspect this is not relevant for the compiler.

Do we need to check anything else, or is this ready for merge?

[Octachron]

The dune linter error is indeed not relevant (the dune file in the compiler tree is exclusively for development purposes).

[mseri]

Thanks!