FIR IDE: Fix completion in property setters

Property consists of getter and setter (both optional). The setter
have a single `value` parameter with type

Because of it, we have to make a separate 'frankenstein setter' with
original resolved header, but with the body of the fake one

It seems that getters does not have such issues

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/BuilderConfigurator.kt

@@ -206,6 +206,7 @@ object BuilderConfigurator : AbstractBuilderConfigurator<FirTreeBuilder>(FirTree
             defaultNull("body")
             default("contractDescription", "FirEmptyContractDescription")
             useTypes(emptyContractDescriptionType)
+            withCopy()
         }
 
         builder(whenExpression) {