Haskell: use `hpack` to populate MAlonzo module names in the .cabal files

[omelkonian]

We currently use an ad-hoc shell command in Makefile:

    find $(HS_DIST)/MAlonzo -name "*.hs" -print\
      | sed "s#^$(HS_DIST)/#        #;s#\.hs##;s#/#.#g"\
      >> $(HS_DIST)/$(CABAL_FILE)

...but we should do it properly using hpack and a package.yaml that generates the .cabal file.