EPA: Add additional comments field to AnnsModule
This is used in exact printing to store comments coming after the
where
keyword but before any comments allocated to imports or decls.
It is used in ghc-exactprint, see https://github.com/alanz/ghc-exactprint/commit/44bbed311fd8f0d053053fef195bf47c17d34fa7
Note: I think this is the last change needed to GHC master to support ghc-exactprint for the GHC 9.10 release.