Cleanup formatting

[gretay-js]

Change make fmt to use dune build @fmt --auto-promote.

• replace all ocamlformat related files in different subdirectories with top-level ones.
• simplify Makefile rules related to formatting
• no need to keep the list of file names to format in 3 different places, now it's just in .ocamlformat-enabled
• no need to keep format settings in sync, they are all in one place
• use .ocamlformat-ignore to exclude flambda2 parser
• it formats dune files too
• vendor "ocaml" to stop it from being formatted.

I'm slightly worried about other consequences of vendoring ocaml: targets that aren't explicitly requested by toplevel dune file won't build or install any more, according to the dune docs), but nothing is missing from the install directory.

[gretay-js]

This is now failing because ocamlformat.yml github workflow we have doesn't set up special dune when doing configure. Why do we have it in a separate workflow file?

[mshinwell]

@gretay-js not sure there is any particularly good reason it's in a separate file

[gretay-js]

@gretay-js not sure there is any particularly good reason it's in a separate file

ok, maybe I can add it as an extra target in one of the existing builds.
The dependency on special dune can probably be avioded, but it's convenient.

[Gbury]

@gretay-js we can probably close this one I think ?

[mshinwell]

@gretay-js ping

[gretay-js]

I'll rebase and fix it up.

[Gbury]

Ping again on that one ?