Include oEmbed endpoints introduced by plugins to the `wp embed provider list`

[garretthyder]

Feature Request

• Yes, I reviewed the contribution guidelines.

Describe your use case and the problem you are facing

Hello,
I noticed the wp embed provider list only contains default WP providers. It would be great if it listed providers added to WP via plugins through wp_oembed_add_provider on the init hook. I tested a few plugins beyond my own and none when added seem to list their providers. Some I tested;
https://en-ca.wordpress.org/plugins/sendtonews-oembed/
https://en-ca.wordpress.org/plugins/jotform-oembed/
https://en-ca.wordpress.org/plugins/github-embed/

In addition to that the wp embed fetch <url> won't work for any oembed URLs of these custom providers.

Describe the solution you'd like

I would love the wp embed functions to cover custom oembed providers installed via plugins to the users WordPress install.

Thank you

[danielbachhuber]

Sounds good 👍 Feel free to submit a pull request, if you'd like. Here is some guidance on our pull request best practices.