oEmbed: Register Gravatar oEmbed provider

[wellyshen]

Description

• To implement 109130-gh-Automattic/gravatar
• Update release version and changelog

Test Instructions

• Check out this PR
• Go to: https://ripe-opossum.jurassic.ninja
  • ID: demo
  • PW: NpwCezDFGMUSWOfRTxc1
• The feature is triggered by copy / paste. So paste a valid Gravatar profile URL, e.g. https://gravatar.com/matt, and you will see the embedded profile card:

[wellyshen]

The embed works well. I noticed there is a style difference between the embed and the hovercard, which I'm not sure is expected: The embed isn't full width like the hovercard, and is slightly indented. This is on 2021. Maybe this is just how 2021 displays embeds?

Yes, the difference is expected. The block’s styles are primarily based on the Figma design for the block / patterns (pWOwbHtbAo6xTO1mTnU0lA-fi-3070-1725). The margins and padding are slightly different (we may need to update to the latest design for the hovercards library), as well as the default width (which can be customized using additional classes or margin settings) and the shadow (which can be adjusted via shadow settings).