Improve aliased struct completions

This PR allows aliased struct to be completed with %. It does so by correcting the subtype of the suggestion.

Fixes #229

lib/elixir_sense/providers/suggestion/complete.ex

@@ -526,7 +526,7 @@ defmodule ElixirSense.Providers.Suggestion.Complete do
         name: name,
         full_name: inspect(mod),
         desc: {"", %{}},
-        subtype: nil
+        subtype: Introspection.get_module_subtype(mod)
       }
     end
   end

test/elixir_sense/providers/suggestion/complete_test.exs

@@ -1452,6 +1452,13 @@ defmodule ElixirSense.Providers.Suggestion.CompleteTest do
     assert entries |> Enum.any?(&(&1.name == "URI"))
 
     assert [%{name: "MyStruct"}] = expand('%ElixirSense.Providers.Suggestion.CompleteTest.')
+
+    env = %Env{
+      aliases: [{MyDate, Date}]
+    }
+
+    entries = expand('%My', env, required_alias: true)
+    assert Enum.any?(entries, &(&1.name == "MyDate" and &1.subtype == :struct))
   end
 
   @tag requires_elixir_1_14: true