oEmbed videos do not allow fullscreen

Problem/Motivation

Embedding a video as media remote_video entity does not allow Fullscreen for the video. On the inner frame it says allowfullscreen=""
To allow fullscreen, it would have to say
allowfullscreen="allowfullscreen"
I cannot find how one would influence this, this must have to do with the Oembed implementation.

Filed as a bug report since Fullscreen is a basic feature IMHO.

Proposed resolution

For the maximum cross-browser compatibility copy youtube and add allowfullscreen allow="fullscreen" to the iframe tag.

This aligns with the iframe documentation - https://developer.mozilla.org/en-US/docs/Web/HTML/Element/iframe

Remaining tasks

Create test for having an iframe from a different sub-domain and set up Gitlab CI to run it.

User interface changes

remote video embeds now are allowed to go fullscreen.

API changes

None

Data model changes

None

Release notes snippet

N/a