Update links to use W3C styling

[s3ththompson]

Off W3C site, use this icon: https://wai-website-theme.netlify.app/components/icons/#external-link

Within W3C site, use this icon: https://wai-website-theme.netlify.app/components/icons/#different-view

[richnoah]

@shawna-slh would you please provide a definition of Off W3C and Within W3C?

[shawna-slh]

Clarification: The icons are optional for when they are useful to inform users — basically, if users would be surprised that a link takes them somewhere else, then good to add an icon to the end of the link.

For links that go within the same resource (in this case, the new APG), no icons are needed.

For links that clearly go elsewhere based on the link text, no icons are needed.

For links that might surprise users going elsewhere -- e.g., to a w3.org/TR/ page -- icons are good.

"Within W3C site" is any w3.org URI
"Off W3C site" is not w3.org