JsonDocLint: Check local ID's in `paths` are also in index.

[aDotInTheVoid]

Would have caught #104064

1. This isn't caught by jsondoclint, although it probably should be. (We can easily add a check that all item's in paths with crate_id 0 (local) are also in in the index.

Originally posted by @aDotInTheVoid in #104064 (comment)