Upstream reftests

[gsnedders]

This is mostly here to have a to-do list for people upstreaming stuff from here. It's not really a bug on the repo per-se. This is also just a blind list of all the folders of reftests; we can probably quickly close a lot of them (who cares about WBXML anyway?).

• [ ] core/standards/bidi/html5bidi
• [ ] core/standards/forms
• [ ] core/standards/mathml/reftests
• [ ] core/standards/wbxml
• [ ] core/standards/web-apps/media
• [ ] core/standards/web-apps/sphinx-canvas (I presume these are Philip`'s old canvas tests)
• [ ] core/standards/wml
• [x] core/standards/xpath (https://github.com/w3c/web-platform-tests/pull/2124)
• [ ] core/standards/xslt-bootstrap
• [ ] core/standards/xslt
• [ ] css/css3/2d-transforms
• [ ] css/css3/flexbox
• [ ] css/css3/gradients
• [ ] css/css3/image-fit
• [ ] css/css3/multicolumn/reftest
• [ ] css/css3/resize
• [ ] css/css3/unprefixed-gradients
• [ ] css/css3/values_and_units
• [ ] css/css3/webfonts
• [ ] css/selectors/reftests

[gsnedders]

cc/ @Ms2ger, @zcorpan

[gsnedders]

core/standards/xpath is being handled in https://github.com/w3c/web-platform-tests/pull/2124