[JS] Inline YouTube, Vimeo and Dailymotion video playback

This proposal is implemented here: https://github.com/microsoft/AdaptiveCards/pull/7112

Problem Statement

Currently, it is not possible to embed a YouTube, Dailymotion, Vimeo (and quite a few other for that matter) video in an Adaptive Card. This feature would make that possible.

Proposed solution

We extend the existing Media element with no schema change. The updated logic does the following:

• If a URL matching a a YouTube, Vimeo or Dailymotion pattern is found in the sources collection, the Media element is setup to embed an inline player instead of the standard HTML5 media player
  • The mimeType property isn't required for YouTube sources
  • If a URL pattern is detected in the sources property, all other sources are ignored
• The Media element will attempt to pull the poster URL automatically from the various providers IF the poster property sin't specified
• As the play button is clicked, the Media element instantiates the embedded player and automatically starts playback

Alternatives or Workarounds

The only alternative currently is to use an image that represents a video thumbnail and to include an OpenURL action somewhere in the card to open the video on the appropriate web site.

Start by reviewing the linked pull request 7112 and the existing Media element implementation. Confirm whether the proposed YouTube, Vimeo, and Dailymotion behavior is already covered, including poster handling and playback, and verify the relevant JavaScript tests if present.