🚀 Feature: Add file path to xunit reporter

[JoshuaKGoldberg]

Feature Request Checklist

• I have read and agree to Mocha's Code of Conduct and Contributing Guidelines
• I have searched for related issues and issues with the faq label, but none matched my issue.
• I want to provide a PR to resolve this

Overview

Filing an issue to track #4985: back in #4219, the json, doc, and json-stream reporters were augmented to output the test filenames in addition to their other attributes. But the xunit reporter wasn't given the same addition.

Suggested Solution

#4985, literally. 😄

As in: adding file: test.file to the reported attributes.

Alternatives

I can't think of anything. https://github.com/mochajs/mocha/pull/4985/files#r1193989943 suggests using test?.invocationDetails?.absoluteFile as a backup, but neither invocationDetails nor absoluteFile exist in Mocha. I think that's a Cypress-only thing.

Additional Info

Adding a co-author credit as @bmish made two PRs justifying this feature. ❤️

Co-authored-by: @bmish