Frontend code for "JUnit XML Test Summary In MR widget"

What does this MR do?

Frontend code for "JUnit XML Test Summary In MR widget":

• Creates an app to render it on the MR widget
• Adds getters and utils to the reports store
• Creates a reusable component to render a code block.

Screenshots (if relevant)

Instructions

Instructions on how to render this locally (it will need the backend work that is on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20576) https://gitlab.com/snippets/1731728#note_91233415

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered

What are the relevant issue numbers?

#45318 (closed)