One step closer to being able to remove `noUncheckedIndexedAccess` in
`packages/richtext-lexical/tsconfig.json`.
I'm introducing UploadData_P4 which is a more precise version of
UploadData. I'm doing it as a different type because there's a chance
it'll be a breaking change for some users.
UploadData is used in many places, but I'm currently replacing it only
in
`packages/richtext-lexical/src/exports/react/components/RichText/converter/converters/upload.tsx`,
because in the other files it's too rooted to other types like
UploadNode.
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