Add compat data for <flex> CSS type (#823)
Add compat data for <flex> CSS type (#823)

* Add <flex> CSS type

* Fix flex value description formatting

* Reconcile `<flex>` (`fr`) type data with `grid-template-*` data

mdn/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data,chrisdavidmills/browser-compat-data,teoli2003/browser-compat-data