ARIA roles in docs and examples

Created by: ffoodd

Questionning documentation markup with accessibility in mind, I came across Scott O'Hara's recent post about implicit landmarks which basically says:

• main role is not necessary anymore since both NVDA and Jaws fill the gap in IE11;
• contentinfo role is useful (albeit not necessary) for macOS VoiceOver with WebKit / Chromium based browsers.

I also added the search role to the search form since it's very useful as a landmark, and obviously updated the vnu-jar.js ignored warning to match what's been done on markup.

There isn't any edge cases as far as I'm aware of, but it's still useful to share the last WebAim Screen-reader users survey (anchored to the browser combos section).

I guess @patrickhlauke should review this?