Add test for impls in typedef

Author: Urgau

src/test/rustdoc-json/typedefs/type_impl.rs

@@ -0,0 +1,12 @@
+#![no_std]
+
+// @has type_impl.json "$.index[*][?(@.name=='Ix')].visibility" \"public\"
+// @has - "$.index[*][?(@.name=='Ix')].kind" \"typedef\"
+pub type Ix = usize;
+
+// @has - "$.index[*][?(@.name=='IxTrait')].visibility" \"public\"
+// @has - "$.index[*][?(@.name=='IxTrait')].kind" \"trait\"
+pub trait IxTrait {}
+
+// @count - "$.index[*][?(@.name=='Ix')].inner.impls" 1
+impl IxTrait for Ix {}