Styling of the MR widget's reports sections

This issue is one of the follow-ups to gitlab-ce#37479. It is part of the effort to improve the readability and overall usability of the MR widget.

In https://gitlab.com/gitlab-org/gitlab-ce/issues/46795, the info, pipeline, and review apps sections of the MR widget were styled. In this issue, only the reports section is to be styled. This includes code quality report, performance metrics report, security reports, and license management report. Approvals and the merge section are to be styled in a later issue.

Design (drafts)

Collapsed	Expanded

Pending design

• Add Tests section (Junit tests)
• Update the design of the reports
• Mobile views based on the prior work in https://gitlab.com/gitlab-org/gitlab-ce/issues/46795