This is an ID-less table with just three columns: an association to the merge
request diff the commit belongs to, the relative order of the commit within the
merge request diff, and the commit SHA itself.
Previously we stored much more information about the commits, so that we could
display them even when they were deleted from the repo. Since 8.0, we ensure
that those commits are kept around for as long as the target repo itself is, so
we don't need to duplicate that data in the database.
The sort orders used to be id_asc / id_desc, and are now created_asc /
created_desc. Users can still have cookies containing the old sort
orders, or bookmarks to links specifying them, so convert these to the
new versions quietly.
Provide more sensible default sort order for issues and merge requests
based on the following table:
| type | state | default sort order |
|----------------|--------|--------------------|
| issues | open | last created |
| issues | closed | last updated |
| issues | all | last created |
| merge requests | open | last created |
| merge requests | merged | last updated |
| merge requests | closed | last updated |
| merge requests | all | last created |
