[core] fix(Tag): remove button has tabIndex if interactive

[mattydono]

multi-select tag remove button now tabs only when tabbing for tag implemented

Fixes #4247

Checklist

• Includes tests
• Update documentation

Changes proposed in this pull request:

Tabbing of the remove button is aligned with the tag itself.

Reviewers should focus on:

Just a quick fix that makes all elements of the tag 'tabbable' or not depending upon whether interactive = true and a tabIndex has been set.

[palantirtech]

Thanks for your interest in palantir/blueprint, @mattydono! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[adidahiya]

looks good but failing format-check... please run yarn format from the root of the repo