OCaml 5.2.0~beta2 packages

[Octachron]

This PR adds the packages for the second (and hopefully last) beta for OCaml 5.2.0.

Exceptionally, this beta contains one Compiler-libs API change (after discussion with the various ocaml development tool teams) concerning the shape API queries. The change is known to break the unreleased support for 5.2.0 in odoc, but I will send a patch to fix that point.

The other changes are more ordinary: we have three bug fixes, and three documentations update.
Thus the release looks in good shape for a prospective full release date in the beginning of May.

---

Changes since the first beta

Compiler-libs API Changes

• 13001: do not read_back entire shapes to get aliases' uids when building the
  usages index
  (Ulysse Gérard, review by Gabriel Scherer and Nathanaëlle Courant)

Bug Fixes

• 13058 Add TSan instrumentation to caml_call_gc(), since it may raise
  exceptions.
  (Fabrice Buoro, Olivier Nicole, Gabriel Scherer and Miod Vallat)

• 13079: Save and restore frame pointer across Iextcall on ARM64
  (Tim McGilchrist, review by KC Sivaramakrishnan and Miod Vallat)

• 13094: Fix undefined behavior of left-shifting a negative number.
  (Antonin Décimo, review by Miod Vallat and Nicolás Ojeda Bär)

Documentation Update

• 13078: update Format tutorial on structural boxes to mention alignment
  questions.
  (Edwin Török, review by Florian Angeletti)

• 13092: document the existence of the [@@poll error] built-in attribute
  (Florian Angeletti, review by Gabriel Scherer)

• 13066, update OCAMLRUNPARAM documentation for the stack size parameter l
  (Florian Angeletti, review by Nicolás Ojeda Bär, Tim McGilchrist, and
  Miod Vallat)

[voodoos]

I updated Merlin 502-preview branch to work with the api changes of this beta release: ocaml/merlin#1727

[avsm]

Thanks!