Add file and speed test properties

[dorny]

This PR adds file and speed properties on test object.

• file was added to json reporter in mocha v7.2.0
• speed was added to json reporter in mocha v8.2.0

I actually tested with even older version of mocha and looks like the properties are available there.

Backstory:
I'm adding mocha support to test-reporter.
Thought it would be nice to have both the console spec reporter output and json report at same time. JSON report would be then processed by test-reporter. Found out it's possible only with mocha-multi-reporters and json-file-reporter. Unfortunately not having file property on test object is a blocker for me.

[ryanrishi]

Thanks @dorny! I'm encountering the same issues using mocha-multi-reporters, writing Mocha results to stdout (via spec) and a file (via json-file-reporter). Unfortunately I can't use Github actions to publish the JSON results because the JSON results don't have a file property.

This PR looks like it will fix this use case.