refactor(turbopack/next-core): Remove uses of generic vc collections (#70815)
Removes the uses of generic vc collections in
`next-core/src/app_structure.rs` and it's callsites.
## Why?
Rather than extended support for `Vc` generics to `ResolvedVc`, I plan
to remove support for them entirely. That means fixing all the callsites
(there's not many).
Removing this is needed to get us to a point where 100% of structs can
be `ResolvedValue`, because structs using these fields cannot otherwise
be ported over to `ResolvedVc`.
## Okay, but Why?
Explained here:
https://github.com/vercel/turborepo/pull/8843#issuecomment-2253158412
I expect removing support for this will decrease the overall size of the
codebase, as the logic for supporting generics is rather complicated.