Group identical code quality issues in MR widget by file
This is an actionable insight from the [UX Department: MRs experience async critique](https://gitlab.com/gitlab-org/ux-research/-/issues/1073) research ([insight][insight]).
### What
In the merge request widget for **code quality**, there is a lot of item duplication. There is no information hierarchy or typography differences.

### Why
With so much duplicated content, it's difficult to focus on what makes each issue different. It also makes it hard to ignore a specific group of similar/identical issues.
### How
Items should be [sorted by severity](https://gitlab.com/gitlab-org/gitlab/-/issues/301121) and then grouped by [category](https://gitlab.com/gitlab-org/gitlab/-/issues/293656#note_1299528441) so that it's easier to parse the list for common issues that can be resolved.
epic