Refactored ConvertMemberToExtension to re-use original declaration instead of regenerating it by text

#KT-4920 Fixed

compiler/frontend/src/org/jetbrains/kotlin/psi/JetPropertyAccessor.java

@@ -59,9 +59,14 @@ public class JetPropertyAccessor extends JetDeclarationStub<KotlinPropertyAccess
         return findChildByType(JetTokens.GET_KEYWORD) != null;
     }
 
+    @Nullable
+    public JetParameterList getParameterList() {
+        return getStubOrPsiChild(JetStubElementTypes.VALUE_PARAMETER_LIST);
+    }
+
     @Nullable
     public JetParameter getParameter() {
-        JetParameterList parameterList = getStubOrPsiChild(JetStubElementTypes.VALUE_PARAMETER_LIST);
+        JetParameterList parameterList = getParameterList();
         if (parameterList == null) return null;
         List<JetParameter> parameters = parameterList.getParameters();
         if (parameters.isEmpty()) return null;