Add trig helper props and some @property props for animation

see https://codepen.io/nocksock/pen/QWXzPQg
which the source file is https://unpkg.com/osc-css@0.2.2/osc.css

h/t @nocksock

Start by reviewing the linked CodePen and its source stylesheet at unpkg.com/osc-css@0.2.2/osc.css to identify the trig helpers and @property declarations being proposed. Then locate the corresponding custom-property files in open-props and determine which additions are required; done means the requested properties are included and covered by the project's existing validation or examples.

Written by the indexing model from the issue text.