Update metadata ready tracking (#67929)
Refactors the `createMetadataComponents` function to convey readiness
via a promise `metadataReady` rather than a renderable component
`<MetadataOutlet>`.
I also moved the resolution out of the render and into the factory
function because we generally only want to do this resolution once and
later we may retry the RSC render and it is wasteful to recompute the
resolved value.
I am instrumenting the ready promise with `status` and `value` so that
in a future update React can unrwap the value synchronously. This isn't
very important right now but in the future we will want to take
advantage of it.
