[mathml-tests] Import MathML tests for the mathvariant attribute. (#4021)

These tests pass in Gecko and WebKit and equivalent tests exist in their test suites.

@karlt Can you please review these tests? They are essentially automatically generated from the unicode.xml file maintained by @davidcarlisle 

View on GitHub: https://github.com/w3c/web-platform-tests/pull/4021

Received on Wednesday, 19 October 2016 09:51:18 UTC