[new-hs-indexer] Track xrefs to modules from import declarations

* Expand xrefs to include `ModuleName` (unfortunately not `Module`)
* Capture these in the indexer
* Expand codemarkup to resolve ModuleName xrefs to Modules

All tested in VS Code, we can click on a module name in an import to
jump to the module.

Author: simonmar

glean/glass/Glean/Glass/SymbolId/Hs.hs

@@ -72,7 +72,10 @@ instance Symbol Hs.NameSort where
 
 instance ToQName Hs.Entity where
   toQName (Hs.Entity_name n) = Glean.keyOf n >>= toQName
-  toQName (Hs.Entity_mod _) = error "TODO: ToQName Hs.Entity_mod"
+  toQName (Hs.Entity_mod mod) = do
+    Hs.Module_key m _ <- Glean.keyOf mod
+    modname <- Glean.keyOf m
+    return $ Right (Name modname, Name "")
   toQName _ = error "ToQName: unknown Hs.Entity"
 
 instance ToQName Hs.Name_key where