Feature request: enforce alphabetical definitions

[N1ark]

Is your feature request related to a problem? Please describe.
It would be nice to allow optionally linting for alphabetical declarations, if annotated. This allows enforcing long lists of independent declaration to remain alphabetically sorted. This facilitates looking for particular definitions. This also facilitates teamwork, as there is only one correct order in which to define things which avoids potential git conflicts over concurrent changes to the same list.

Describe the solution you'd like
Marking the start-end of the declaration list with comments would be sufficient:

(* @ocamlformat alphabetical-start *)
let pexp_apply x y = pexp_apply ~loc:(get_loc ()) x y
let pexp_construct x y = pexp_construct ~loc:(get_loc ()) x y
let pexp_field x y = pexp_field ~loc:(get_loc ()) x y
let pexp_ident x = pexp_ident ~loc:(get_loc ()) x
let pexp_match x y = pexp_match ~loc:(get_loc ()) x y
let pexp_record x y = pexp_record ~loc:(get_loc ()) x y
(* @ocamlformat alphabetical-end *)

I'm aware ocamlformat also supports attributes, so maybe something like this would be more OCaml-esque :)

[@@@ocamlformat "alphabetical=start"]
let pexp_apply x y = pexp_apply ~loc:(get_loc ()) x y
let pexp_construct x y = pexp_construct ~loc:(get_loc ()) x y
let pexp_field x y = pexp_field ~loc:(get_loc ()) x y
let pexp_ident x = pexp_ident ~loc:(get_loc ()) x
let pexp_match x y = pexp_match ~loc:(get_loc ()) x y
let pexp_record x y = pexp_record ~loc:(get_loc ()) x y
[@@@ocamlformat "alphabetical=end"]

Additional context
Rust has a similar feature, with tidy::alphabetical; it is widely used in the ecosystem and even within the compiler itself. it looks like this in practice:

// tidy-alphabetical-start
fn aaa() {}
fn eee() {}
fn z() {}
// tidy-alphabetical-end

[EmileTrotignon]

If we do this it should definitely be done with attributes.

I have wanted this before, never enough to try and add it, but its definitely useful. We don't really have things like that in ocamlformat, so it feels a bit out of scope, but it would be difficult to get the functionality with an external tool.

A bigger issue is that ocamlformat currently guarantees that the formatting will not change the AST (and therefore the semantics) in 100% of cases. There is a check that crashes instead of formatting if an AST change is produced. This breaks this invariant, and even if its only when its called for.

I just noticed the rust tool is part of a linter and not a formatter, and honestly it would be more appropriate. The way I'd go about doing that is to make a linter with ppxlib, and an lsp/editor extension.