[FIR/IR generator] Factor out walkableChildren and transformableChildren

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

@@ -112,7 +112,6 @@ class FieldWithDefault(val origin: Field) : Field() {
     override var withGetter: Boolean = false
     override var customSetter: String? = null
     override var fromDelegate: Boolean = false
-    var needAcceptAndTransform: Boolean = true
     override val overridenTypes: MutableSet<TypeRefWithNullability>
         get() = origin.overridenTypes
 

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

@@ -64,12 +64,6 @@ class Implementation(val element: Element, val name: String?) : FieldContainer,
     override val hasTransformChildrenMethod: Boolean
         get() = true
 
-    override val walkableChildren: List<FieldWithDefault>
-        get() = allFields.filter { it.containsElement && !it.withGetter && it.needAcceptAndTransform }
-
-    override val transformableChildren: List<FieldWithDefault>
-        get() = walkableChildren.filter { it.isMutable }
-
     override fun get(fieldName: String): FieldWithDefault? {
         return allFields.firstOrNull { it.name == fieldName }
     }

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

@@ -159,6 +159,7 @@ fun SmartPrinter.printImplementation(implementation: Implementation) {
                     println()
                     withIndent {
                         for (field in walkableFields) {
+                            check(field is FieldWithDefault)
                             when (field.name) {
                                 "explicitReceiver" -> {
                                     val explicitReceiver = implementation["explicitReceiver"]!!
@@ -225,6 +226,7 @@ fun SmartPrinter.printImplementation(implementation: Implementation) {
                 if (!isInterface && !isAbstract) {
                     printBlock {
                         for (field in transformableChildren) {
+                            check(field is FieldWithDefault)
                             when {
                                 field.name == "explicitReceiver" -> {
                                     val explicitReceiver = implementation["explicitReceiver"]!!