OCaml 4.14.0, first alpha release

[Octachron]

This PR adds the base and variants+option package for the first alpha release of OCaml 4.14.0.

As discussed, I have added the --docdir=%{doc}%/ocaml" configure option to account for ocaml/ocaml#10669 .

Like with the 4.13.0~alpha1 packages, I have updated the ocaml meta-package constraints to allow installation.

[kit-ty-kate]

Successfully tested locally. Thanks a lot! 🎉

[dbuenzli]

What happend to the --docdir ? I wanted to odig the 4.14 release notes but got nothing:

> ls $(opam var ocaml:doc)
ls: /Users/dbuenzli/.opam/4.14.0/doc/ocaml: No such file or directory

[kit-ty-kate]

arf, mmh, it looks like the option disappeared from the opam file between the last rc and the final release :/
Could you open a PR to add it to the 4.14.0 packages and cc @Octachron and @dra27 in it for double-check?

[dbuenzli]

Could you open a PR to add it to the 4.14.0 packages

It's not obvious to me were that's supposed to happen (and a bit in a hurry right now):

> opam info --raw ocaml.4.14.0 | grep build: -C 2
  [OCAML_TOPLEVEL_PATH = "%{toplevel}%"]
]
build: [
  "ocaml" "%{ocaml-config:share}%/gen_ocaml_config.ml" _:version _:name
]

[dra27]

See #21890.