[tree generator] Rename AbstractImplementation.fieldsWith(out)Default

to better describe their intended usage, see also next commit.

^KT-65773 In Progress

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

@@ -72,7 +72,7 @@ internal class ImplementationPrinter(
                         && !element.typeName.endsWith("AnnotationsContainer")
             }.orEmpty()
 
-            val customCalls = fieldsWithoutDefault.filter { it.customInitializationCall != null }
+            val customCalls = fieldsInConstructor.filter { it.customInitializationCall != null }
             if (bindingCalls.isNotEmpty() || customCalls.isNotEmpty()) {
                 println()
                 println("init {")