### What?
`next build` is incorrectly reporting file size stats for the root path
when using the app dir
### Why?
In #50768, the denormalization logic was removed for appDir routes, but
`pagesManifest` has the root page keyed by `/` while the actual path
will be `/index`.
### How?
This re-adds a simpler denormalize function that just replaces `/index`
with `/`.
semi-related: #42819Fixes#51692
link NEXT-1306
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Co-authored-by: JJ Kasper <jj@jjsweb.site>
Co-authored-by: Jiachi Liu <inbox@huozhi.im>
aec75c2f06