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/gen/org/jetbrains/kotlin/fir/declarations/builder/FirPropertyAccessorBuilder.kt

@@ -79,3 +79,25 @@ inline fun buildPropertyAccessor(init: FirPropertyAccessorBuilder.() -> Unit): F
     }
     return FirPropertyAccessorBuilder().apply(init).build()
 }
+
+@OptIn(ExperimentalContracts::class)
+inline fun buildPropertyAccessorCopy(original: FirPropertyAccessor, init: FirPropertyAccessorBuilder.() -> Unit): FirPropertyAccessor {
+    contract {
+        callsInPlace(init, kotlin.contracts.InvocationKind.EXACTLY_ONCE)
+    }
+    val copyBuilder = FirPropertyAccessorBuilder()
+    copyBuilder.source = original.source
+    copyBuilder.session = original.session
+    copyBuilder.resolvePhase = original.resolvePhase
+    copyBuilder.origin = original.origin
+    copyBuilder.returnTypeRef = original.returnTypeRef
+    copyBuilder.valueParameters.addAll(original.valueParameters)
+    copyBuilder.body = original.body
+    copyBuilder.contractDescription = original.contractDescription
+    copyBuilder.symbol = original.symbol
+    copyBuilder.isGetter = original.isGetter
+    copyBuilder.status = original.status
+    copyBuilder.annotations.addAll(original.annotations)
+    copyBuilder.typeParameters.addAll(original.typeParameters)
+    return copyBuilder.apply(init).build()
+}

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) {