[FIR generator] Print builder property name in generated classes' KDocs

Just like we do when generating the IR tree

generators/tree-generator-common/src/org/jetbrains/kotlin/generators/tree/AbstractElement.kt

@@ -16,6 +16,11 @@ abstract class AbstractElement<Element, Field> : ElementOrRef<Element, Field>, F
 
     abstract val name: String
 
+    /**
+     * The fully-qualified name of the property in the tree generator that is used to configure this element.
+     */
+    abstract val propertyName: String
+
     abstract val kDoc: String?
 
     abstract val fields: Set<Field>

generators/tree-generator-common/src/org/jetbrains/kotlin/generators/tree/printer/printUtils.kt

@@ -67,3 +67,12 @@ fun SmartPrinter.printKDoc(kDoc: String?) {
     }
     println(" */")
 }
+
+fun AbstractElement<*, *>.extendedKDoc(defaultKDoc: String? = null): String = buildString {
+    val doc = kDoc ?: defaultKDoc
+    if (doc != null) {
+        appendLine(doc)
+        appendLine()
+    }
+    append("Generated from: [${element.propertyName}]")
+}