Add interactive-widget to known viewport properties

[BenjaminAster]

Chromium now supports the interactive-widget property in the viewport meta tag. However, Lighthouse throws a warning when using it.

[connorjclark]

Thanks for the issue!

We'll need to update https://github.com/dontcallmedom/metaviewport-parser/ - an example of adding a new property there: https://github.com/dontcallmedom/metaviewport-parser/pull/6/files