VI-style up/down navigation in commit lists
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### Description
- Use `j` and `k` on the keyboard to move down and up, respectively, through a list of commits, and then press `Enter` to navigate into the commit.
- Similar to VI keyboard shortcuts.
- Implement this for (1) commit list view for a branch and (2) commit list view in a merge request.
- This allows a person to quickly navigate through a list of commits using just the keyboard, similar to triaging emails in Gmail / Inbox.
### Examples from GitHub
- GitHub has this in the branch commit list view and the pull request commit list view.
- GitHub has this in their file browser view for file navigation.
- GitHub has this in their pull requests list view for navigation.
- GitHub has this in their issues list view for navigation.

### Related
- https://gitlab.com/gitlab-org/gitlab-ce/issues/32310
- https://gitlab.com/gitlab-org/gitlab-ce/issues/32311
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