Switch the default revealOrder to "forwards" and tail "hidden" on SuspenseList (#35018)

We have warned about this for a while now so we can make the switch.

Often when you reach for SuspenseList, you mean forwards. It doesn't
make sense to have the default to just be a noop. While "together" is
another useful mode that's more like a Group so isn't so associated with
the default as List. So we're switching it.

However, tail=hidden isn't as obvious of a default it does allow for a
convenient pattern for streaming in list of items by default.

This doesn't yet switch the rendering order of "backwards". That's
coming in a follow up.