Add all element attributes for the MetaElements artifacts

[roelfjan]

Feature request summary
Now for the MetaElements artifact the properties name and content are provided (see: types). I would like to get all attributes on the <meta> element.

Facebook uses the attribute property instead of name for their tags, like this:

<meta property="og:description" content="[description]" />

Which results in the MetaElements like this:

 { name: "", content: "[description]" }

I would like to receive something like this for a Facebook meta tag:

 { property: "og:description", content: "[description]" }

What is the motivation or use case for changing this?
I am creating a Lighthouse plugin for an audit on social sharing tags like Twitter and Facebook present on the page. This feature is needed for a check on Facebook tags.

How is this beneficial to Lighthouse?
This feature provides a better representation of the audited page. Which will provide Lighthouse users with more information.

[patrickhulce]

I'm not sure about all the attributes but property definitely sounds good! I'd welcome such a PR :)

[connorjclark]

fyi https://stackoverflow.com/questions/22350105/whats-the-difference-between-meta-name-and-meta-property