Notice: Updating OCaml + Dependencies

[WardBrian]

Hi all -

This post is in preparation for #1019, which bumps our OCaml version to 4.12.0 and bumps several dependencies. @serban-nicusor-toptal and I are sorting out the last steps of the CI transition now.

This impacts all current developers in the following ways:

• You will need to re-run the setup scripts for opam and the dependencies. If you already have a working development environment (meaning you have opam installed), the following should be enough:
  opam update && opam switch create 4.12.0
opam install -y core_kernel.v0.14.2 menhir.20210929 ppx_deriving.5.2.1 fmt.0.8.8 yojson.1.7.0
opam install -y ocamlformat.0.19.0 merlin ocaml-lsp-server utop ocp-indent patdiff odoc

• ocamlformat has updated. This leads to changes in almost every file.

• ocaml-lsp-server is now available alongside Merlin as a developer/IDE tool

This is just intended as an easy way to let everyone know, so I'm going to ping here everyone who has made contributions in the past 1 year:

@SteveBronder @rok-cesnovar @rybern @adamhaber @nhuurre @seantalts @bbbales2 @nickdidio @mandel @spinkney

If you have the chance, I recommend performing the steps in the first bullet whenever is convenient. You will still be able to use opam switch to go back to the current switch (most likely named 4.07.0) and continue using that until the PR is officially merged.

[WardBrian]

Here's a brief guide for rebasing/merging existing changes after this is merged:

1. Make sure you have an updated opam environment (first bullet above)
2. Merge/rebase and prefer your changes (assuming you were up to date with master before this).
3. Try to build. If you get errors about int expected near the use of =, <>, <=,etc, add open Core_kernel.Poly under the open of Core_kernel. If you get other errors, check if anything similar changed in this commit
4. Run ocamlformat
5. Merge should be pretty clean after this.