Environment in Typechecker plugins does not match the passed in one

When using typeCheckResultAction to write a type checker plugin the explicitly passed TcGblEnv and the TcGblEnv from the environment do not match up. The definition of typeCheckResultAction currently is

  , typeCheckResultAction :: [CommandLineOption] -> ModSummary -> TcGblEnv
                               -> TcM TcGblEnv
    -- ^ Modify the module when it is type checked. This is called at the
    -- very end of typechecking.

In a plugin implementation one would expect

typeCheckResultAction = \_ _ tcg_gbl_env -> do 
  env <- getGblEnv
  assert (env == tcg_gbl_env)

to hold but currently the TcGblEnv from the environment doesn't contain

1. the module doc header
2. the renamed exports (and export list)

(A workaround is to use setGblEnv tcg_gbl_env here but it sure is unexpected)

See !4766 (closed) for a fix.