Fix edge case in type hashing (#10601) [backport]

Empty types introduced by a template produced the same hash of the
"clean" type sharing the same name.

tests/ccgbugs/tsighash_typename_regression.nim

@@ -15,3 +15,18 @@ proc foo[T](t: T) =
 
 foo(123)
 foo("baz")
+
+# Empty type in template is correctly disambiguated
+block:
+  template foo() =
+    type M = object
+      discard
+    var y = M()
+
+  foo()
+
+  type M = object
+    x: int
+
+  var x = M(x: 1)
+  doAssert(x.x == 1)