[6.x] Augment video fields to a value object carrying the provider

[edalzell]

The video fieldtype doesn't implement augment(), so the raw string is all a template ever gets. There's no provider discriminator, and no first-class way to get an embed URL — {{ video_field | embed_url }} works only because CoreModifiers::embedUrl() happens to know how to rewrite YouTube and Vimeo URLs by hand.

This augments to a Statamic\Fieldtypes\Video\Video value object exposing provider, id, url and embed_url, following the ArrayableString/ArrayableLink convention: __toString() returns the original value, so {{ video_field }} is unchanged, and it implements Arrayable, ArrayAccess, Boolable and JsonSerializable. It recognises YouTube, Vimeo, direct video files (via FileTypes::video()) and cloudflare:<id> values, falling back to an unsupported provider.

The YouTube/Vimeo URL→embed logic is moved out of CoreModifiers::embedUrl() onto the value object, and the modifier now delegates to it — one implementation rather than two. embedUrl, trackableEmbedUrl and isEmbeddable also accept the object directly. The existing modifier tests pass unchanged, which is the regression proof for the move.

Worth a look: augment() returns the object for all values, including plain URLs. __toString() covers direct output, modifiers and GraphQL (the existing GraphQL test still passes unchanged), but a strict is_string() check downstream would now see an object. Happy to keep plain URLs as strings and only return the object for cloudflare: values if you'd rather not change that surface in a major.

Split out of #11871 so the augmentation contract can be settled on its own, ahead of the Cloudflare Stream and oEmbed work. No new dependencies.