EPA: Add additional comments field to AnnsModule

Alan Zimmermanrequested to merge
wip/az/epa-hsmodule-ann-cs into master

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.

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