Relativize spec paths more when reporting

[50Wliu]

Requirements

• Filling out the template is required. Any pull request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion.
• All new code requires tests to ensure against regressions

Description of the Change

First, here's a before/after comparison on Windows:

Before	After

Much nicer.

Changes include:

• Updating to the new .<anonymous> syntax
• Stripping away file:/// identifiers on Windows paths and converting the rest of the path to use Windows path separators (in order for it to get relativized correctly)
• Relativizing paths in parentheses

Alternate Designs

Instead of relativizing the path twice, depending on if its in parentheses or not, a more general line.replace(///#{_.escapeRegExp(spec.specDirectory}#{_.escapeRegExp(path.sep}///, '') could be used. I am unsure if that would potentially relativize more than we wanted.

Why Should This Be In Core?

Because it fixes already-implemented code in core.

Benefits

See before/after picture above.

Possible Drawbacks

I don't foresee any.

Applicable Issues

None.

/cc @damieng for the Windows portions.

[50Wliu]

If specs are necessary for this change I can add them.

[damieng]

This looks good to me. I'm okay with keeping windows-style paths for local stuff although for the areas where we report remotely - bugsnag, GA, notification to github issue - I prefer to normalize them to Unix style so that they are correctly combined into a single issue where appropriate.

Thanks for this!