The localize_d7_comment migration needs 'comment' as module dependency.

The question was raised by Guiu what happens to the migration when we uninstall and reinstall comment module.
It is quite simple, because the migration is in config/optional:
(that is if the dependency is present as in the MR)
- When we uninstall comment module (if no migration has started yet), the migration config entity is gone.
- When we install comment module, while l10n_migrate is enabled, the migration config entity comes back.

I have not checked what happens if there is already a migration based on the config entity.
In my own experiment, the migration would not work anyway because I did not set up the source database.

However, there are some other observations:
- The l10n_migrate module currently depends on migrate_tools via l10n_migrate.info.yml. That module is not present via composer.json require-dev. This should be investigated further.
- To uninstall comment module, one must first uninstall fields that reference comments.

This said, I don'T see that any of the above would be a blocker to adding this dependency in the migration.

Btw I don't really know if we need that "enforced" part.

dependencies:
  enforced:
    module:
      - comment

vs

dependencies:
  module:
    - comment

See https://www.drupal.org/node/2404447

From how I understand it:
If we would let Drupal save the migration config entity, then dependencies are re-calculated. Any non-enforced dependency can be lost, and new non-enforced dependencies could be added, based on the plugins being used.
Having the dependency "enforced" means that we are fully in control, and Drupal is not allowed to remove it when it re-calculates dependencies.
However, for migration config entities, we typically don't allow Drupal to do anything, we only edit them by hand. At least this is how I remember working with migrate_plus migration config entities.
So in our case there is no practical scenario when the "enforced" would make a difference. But it is still safer and more correct, if we manually add a dependency, that we add it as "enforced".