[FIR/IR generator] Move usedTypes to AbstractElement, rename it

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

@@ -166,6 +166,15 @@ abstract class AbstractElement<Element, Field, Implementation>(
         }
     }
 
+    /**
+     * Types/functions that you want to additionally import in the file with the element class.
+     *
+     * This is useful if, for example, default values of fields reference classes or functions from other packages.
+     *
+     * Note that classes referenced in field types will be imported automatically.
+     */
+    val additionalImports = mutableListOf<Importable>()
+
     final override fun get(fieldName: String): Field? {
         return allFields.firstOrNull { it.name == fieldName }
     }

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

@@ -31,6 +31,7 @@ abstract class AbstractElementPrinter<Element : AbstractElement<Element, Field,
 
     context(ImportCollector)
     fun printElement(element: Element) {
+        addAllImports(element.additionalImports)
         printer.run {
             val kind = element.kind ?: error("Expected non-null element kind")
 

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

@@ -42,7 +42,14 @@ abstract class AbstractImplementation<Implementation, Element, Field>(
 
     override val packageName = element.packageName + ".impl"
 
-    val usedTypes = mutableListOf<Importable>()
+    /**
+     * Types/functions that you want to additionally import in the file with the implementation class.
+     *
+     * This is useful if, for example, default values of fields reference classes or functions from other packages.
+     *
+     * Note that classes referenced in field types will be imported automatically.
+     */
+    val additionalImports = mutableListOf<Importable>()
 
     init {
         @Suppress("UNCHECKED_CAST")

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

@@ -32,6 +32,7 @@ abstract class AbstractImplementationPrinter<Implementation, Element, Implementa
 
     context(ImportCollector)
     fun printImplementation(implementation: Implementation) {
+        addAllImports(implementation.additionalImports)
         printer.run {
             buildSet {
                 if (implementation.requiresOptIn) {

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

@@ -156,7 +156,7 @@ abstract class AbstractImplementationConfigurator<Implementation, Element, Imple
          * Note that classes referenced in field types will be imported automatically.
          */
         fun additionalImports(vararg importables: Importable) {
-            importables.forEach { implementation.usedTypes += it }
+            implementation.additionalImports.addAll(importables)
         }
 
         /**