[tree generator] Allow adding kDocs to implementation classes

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

@@ -48,6 +48,8 @@ abstract class AbstractImplementation<Implementation, Element, Field>(
      */
     val additionalImports = mutableListOf<Importable>()
 
+    var kDoc: String? = null
+
     init {
         @Suppress("UNCHECKED_CAST")
         element.implementations += this as Implementation

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

@@ -8,6 +8,7 @@ package org.jetbrains.kotlin.generators.tree
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.generators.tree.printer.braces
 import org.jetbrains.kotlin.generators.tree.printer.printBlock
+import org.jetbrains.kotlin.generators.tree.printer.printKDoc
 import org.jetbrains.kotlin.generators.tree.printer.typeParameters
 import org.jetbrains.kotlin.utils.SmartPrinter
 import org.jetbrains.kotlin.utils.addToStdlib.ifNotEmpty
@@ -37,6 +38,7 @@ abstract class AbstractImplementationPrinter<Implementation, Element, Implementa
     fun printImplementation(implementation: Implementation) {
         addAllImports(implementation.additionalImports)
         printer.run {
+            printKDoc(implementation.kDoc)
             buildSet {
                 if (implementation.requiresOptIn) {
                     add(implementationOptInAnnotation)

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

@@ -142,6 +142,10 @@ abstract class AbstractImplementationConfigurator<Implementation, Element, Imple
             implementation.isPublic = true
         }
 
+        fun kDoc(kDoc: String) {
+            implementation.kDoc = kDoc
+        }
+
         private fun getField(name: String): ImplementationField {
             return implementation.getField(name)
         }