Persist name resolution for measure names

[facundominguez]

Another step for #2169

Name resolution of measures is now remembered when importing specs.

Measures now use the same module aliases as the modules from which they are imported. For instance, foo is not in scope in module Test, but M.foo is.

module ModuleBar where
{-@ measure foo :: Bool @-}

---
module Test where
import qualified ModuleBar as M
{-@ lemma :: { foo } @-}
lemma :: ()
lemma = ()

import qualified ModuleBar as M brings into scope M.foo and any other measure exported or reexported from M with alias M.. Measures exported from module M_LHAssumptions are also exposed with alias M. if M_LHAssumptions is not imported explicitly.

Ambiguities are reported if multiple measures are in scope with the same name when the name is used.