[Feature request] [Merge requests] View old comments on merge request versions

Description

Merge request versions currently bail comments out to the discussions tab and don't show them on the diff itself. However it would be very useful to see these comments in the context of a new diff pushed to 'fix' the comments.

If someone made a commend on merge request version A, I'd like to be able to see that that was addressed in merge request version B - i.e. when looking at the A..B version show the comments that were made on A. - Otherwise the only way to find those comments is to randomly expand the 'outdated diff' sections til you find them

Proposal

As above

Links / references

Potentially relates to improving the diff versioning with interdiff: https://gitlab.com/gitlab-org/gitlab-ce/issues/23269

Originally mentioned here: https://gitlab.com/gitlab-org/gitlab-ce/issues/19049