Add BarProp API (#7629)
Add BarProp API (#7629)

This PR is a part of a project to add missing interfaces and interface features to BCD that are from a spec in Editor's Draft or more and is supported in at least one browser.  This particular PR adds missing features, populating the results using data from the [mdn-bcd-collector](https://mdn-bcd-collector.appspot.com) project (v1.1.6), for the BarProp API.

Spec: https://html.spec.whatwg.org/multipage/window-object.html#barprop
IDL: https://github.com/w3c/webref/blob/master/ed/idl/html.idl
mdn/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data