Sharing: move Enhanced Open Graph into the basic Open Graph functions

Jetpack uses 2 different files to generate Open Graph Meta tags:
- The first one, `functions.opengraph.php`, is used as soon as you use either Sharing or Publicize, and as long as you don't use a conflicting plugin.
- The second, `enhanced-open-graph.php`, hooks into the `jetpack_open_graph_tags` filter that is used to render the tags, and is only used when the Publicize module is active.

The file includes the following features (functions):
- Better OG Image Tags for Image Post Formats (`enhanced_og_image`)
- Better OG Image Tags for Gallery Post Formats (`enhanced_og_gallery`)
- Allows VideoPress, YouTube, and Vimeo videos to play inline on Facebook (`enhanced_og_video`)

I think it would make sense to offer these functions to everyone using the Open Graph Meta tags, even if they don't use the Publicize module.

@justinshreve It seems you originally merged that file back from WordPress.com. Can you recall why it wasn't added to the original tags?

Start by reading functions.opengraph.php and enhanced-open-graph.php, including enhanced_og_image, enhanced_og_gallery, and enhanced_og_video. Trace how jetpack_open_graph_tags is registered for Sharing and Publicize, then verify that these enhancements are available whenever Open Graph tags are enabled, without changing existing tag output unexpectedly.

Written by the indexing model from the issue text.