…3331)

I believe that these mean the same thing. We don't have to emit the
attribute if it's `none` for these cases because if there is no matching
scenario we won't apply the animation in this case.

The only case where we have to emit `none` in the attribute is for
`vt-update` because those can block updates from propagating upwards.

Follow up to #33293.

This solves a race condition when boundaries are added to the batch
after the `startViewTransition` call.

This doesn't matter yet but it will once we start assigning names before
the `startViewTransition` call.

A possible alternative solution might be to ensure the names are added
synchronously in the event that adds to the batch. It's possible to keep
adding to a batch until the snapshot has happened.

#33332)

Stacked on #33330.

This walks the element tree to activate the various classes under
different scenarios. There are some edge case things that are a little
different since we can't express every scenario without virtual nodes.

The main thing that's still missing though is avoiding animating updates
if it can be contained to a layout or enter/exit/share if they're out of
the viewport. I.e. layout stuff.