`CacheNode.data` is used to lazily kick off a request during render, and
represents the result of the entire Flight response. It doesn't
correspond directly to the RSC data of the cache node itself — that's
`subTreeData`. To complicate things further, I'm about to add another
field to CacheNode that represents prefetched RSC data.
To make it a little less confusing, I've renamed the `data` field to
`lazyData`. Still not perfectly clear on first glance, but it's at least
more specific. With PPR, the goal is to remove the lazy data fetching
mechanism in favor of initiating the request immediately upon
navigation. So this field will eventually go away.
In the next PR, I will rename `subTreeData`, too. Perhaps something with
"rsc" in the name so it's less generic than "data".
Closes NEXT-1843
c2ab5f704a