Resolve polymorphic bindings in the the function type

Partially evaluated functions use elabTypes to generate the type
signature of the argument; this needs to resolve polymorphic bindings in
order to type-check subsequent expressions.

Belonging to [master]:
  - OpenModelica/OMCompiler#2283
  - OpenModelica/OpenModelica-testsuite#878

Compiler/FrontEnd/Static.mo

@@ -8566,6 +8566,7 @@ algorithm
       outDimensions := slotsVectorizable(outSlots, inInfo);
       outResultType := res_ty;
       outFunctionType := DAE.T_FUNCTION(params, outResultType, func_attr, path);
+      outFunctionType := Types.fixPolymorphicRestype(outFunctionType, pb, inInfo);
 
       // Only created when not checking types for error msg.
       outFunctionType := createActualFunctype(outFunctionType, outSlots, inCheckTypes);