[6.x] Render direct video files in a video element

[edalzell]

A direct video URL like https://example.com/clip.mp4 is rendered inside an <iframe> — the same element used for YouTube and Vimeo — so it gets no playback controls and relies on whatever the browser decides to do with a bare video document.

The component already distinguishes these via its isVideo computed, so this renders them in a real <video controls> element instead. Lazy-loading behaviour is unchanged; the src is still gated on isVisible.

Split out of #11871 so it can land on its own.

[jasonvarga]

This needs a rebase and conflict resolution now because of #15456

[jasonvarga]

PS. In every browser I tried to load a direct mp4 file, the iframe seemed to include video controls (on 6.x). Was there a specific situation where this was helping?

Regardless, this looks fine.

[edalzell]

You're right, and my premise was wrong. I checked in Chromium: pointing an iframe at an .mp4 makes the browser render its built-in viewer, which is literally <video controls autoplay name="media">. So controls have been there all along — I asserted otherwise without verifying it.

What's actually left is too thin to justify the change: the iframe viewer sets autoplay (Chromium's autoplay policy blocks it, so no visible difference today) and <video> avoids a nested browsing context. Not worth a PR on its own.

Closing this. The <video> branch still appears in #15460, but there it's doing real work — the server classifies the value, so the component knows it's a file rather than guessing from .mp4 being somewhere in the string, which also catches ?foo=.mp4.