Fix forward declaration issues in template/macro context (#15091)

* Fix forward declaration issues in template/macro context

* Correct forward declaration resolving for overloads

* Remove old dead code

* WIP consistent gensym ids

* Minimize diff

* Remove obsoleted hack

* Add templInstCounter to give unique IDs to template instantiations

* Remove obsoleted code

* Eh, init in myOpen, not myProcess...

* Remove optNimV019

* Add testcase for #13484

compiler/types.nim

@@ -936,7 +936,7 @@ proc equalParams(a, b: PNode): TParamsEquality =
         discard
       of paramsIncompatible:
         result = paramsIncompatible
-      if (m.name.id != n.name.id):
+      if m.name.id != n.name.id:
         # BUGFIX
         return paramsNotEqual # paramsIncompatible;
       # continue traversal! If not equal, we can return immediately; else