dev-deps target does not consider the edition in the toml file

[Halbaroth]

If I run make dev-deps in a project that requires a specific version of OCaml, drom will install
all the dev dependencies in the current opam switch without checking that the version of OCaml is correct.

There is an inconsistency between build-deps and dev-deps. The former creates a local switch if it does not already exist. The latter installs everything in the current switch.

I guess that the expected usage is to run these commands:

make build-deps
eval $(opam env) 
make dev-deps

This workflow has several issues:

1. We have to call opam env, which is very annoying and even worse on Windows...
2. Sometimes dev-deps will introduce more constraints on packages installed by build-deps, so we have to recompile them again...
3. It is counterintuitive that dev-deps is not an extension of build-deps.

In my opinion, we should:

• Emit an error if the minimal edition of the toml file is not satisfied by the current switch.
• Create a local switch with dev-deps too with the edition version of OCaml for instance.
• Only use a local switch and wrap every calls of opam to ensure that we only modify this local switch.