Manifest (1): lib_test, lib_stdlib, lib_lwt_result_stdlib

Context

This is a small subset of !3366 (merged), which aims at generating dune and .opam files from a manifest.ml file. See !3366 (merged) for a broad view of the end goal.

Because !3366 (merged) is too large to review in one go, the plan is to make several MRs targetting subparts of the dune and .opam files, without the generator itself. The goal is to check all changes in dune and .opam files made by !3366 (merged). Even if we do not merge !3366 (merged) ever, we'll fix some inconsistencies dune and .opam files this way. After all changes to dune and .opam files have been reviewed and merged, we can merge the generator itself and easily see that it generates the exact same files.

This MR contains the subset of !3366 (merged) for:

• lib_test
• lib_stdlib
• lib_lwt_result_stdlib

It can be seen as a warm-up MR. The changes are easy to review:

• whitespace is a bit different (since the code is generated and not human-written);
• some version number constraints are made consistent with other existing packages;
• a {with-test} was added to a dependency that is only used by tests.

The latter ({with-test}) is an example of inconsistency that is automatically fixed by using the generator.

Manually testing the MR

Compile everything (or let the CI do it for you).

Checklist

• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR