[IR] Support specifying kdocs for properties in IR tree generator

compiler/ir/ir.tree/tree-generator/src/org/jetbrains/kotlin/ir/generator/config/ConfigModel.kt

@@ -91,6 +91,8 @@ sealed class FieldConfig(
     var printProperty = true
     var strictCastInTransformChildren = false
 
+    var kdoc: String? = null
+
     var generationCallback: (PropertySpec.Builder.() -> Unit)? = null
 
     override fun toString() = name

compiler/ir/ir.tree/tree-generator/src/org/jetbrains/kotlin/ir/generator/model/Model.kt

@@ -84,6 +84,8 @@ sealed class Field(
     var needsDescriptorApiAnnotation = false
     abstract val transformable: Boolean
 
+    val kdoc = config?.kdoc
+
     val printProperty = config?.printProperty ?: true
     val generationCallback = config?.generationCallback
 

compiler/ir/ir.tree/tree-generator/src/org/jetbrains/kotlin/ir/generator/print/Elements.kt

@@ -67,6 +67,10 @@ fun printElements(generationPath: File, model: Model) = sequence {
                         addAnnotation(descriptorApiAnnotation)
                     }
 
+                    field.kdoc?.let {
+                        addKdoc(it)
+                    }
+
                     field.generationCallback?.invoke(this)
                 }.build())
             }