Add file path to `xunit` reporter

[bmish]

Description of the Change

Expose test file path for each test case in the xunit reporter.

<testsuite name="Mocha Tests" tests="2" failures="0" errors="0" skipped="0" timestamp="Tue, 17 May 2022 21:10:34 GMT" time="0.001">
<testcase classname="Array #indexOf()" name="should return -1 when the value is not present" file="/path/to/test/array.js" time="0"/>
<testcase classname="Set #has()" name="should return false when the value is not present" file="/path/to/test/set.js" time="0"/>
</testsuite>

Alternate Designs

Why should this be in core?

The test file path was already added to other reporters in this PR:

• https://github.com/mochajs/mocha/pull/4219

It seems the file path can be added to each reporter as needed.

Benefits

• Can be easier to find test file from file path instead of just test name, especially when overlapping/similar/identical test names are present, or in a large codebase
• In particular, it can be easier for automated tooling to find the test file from the file path as opposed to the test name when performing test analysis or other scripting

Possible Drawbacks

• Greater size / noise of output for people who don't need the file path
• Let me know if there's any other reason not to do this

Applicable issues

None.

This should be part of a minor release as an enhancement.

[github-actions[bot]]

This PR hasn't had any recent activity, and I'm labeling it stale. Remove the label or comment or this PR will be closed in 14 days. Thanks for contributing to Mocha!

[villelahdenvuo]

I would love to have this for splitting tests on the CI!

[bmish]

@villelahdenvuo I just reopened the PR as #4985. Please comment or upvote the PR to express interest.