[IR] Make IrMutableAnnotationContainer an IrElement

It is required, so that IR tree generator will properly handle
the `annotations` property in subsequent commits,
e.g., to include them in implementation classes.

All subclasses of IrMutableAnnotationContainer
do already derive from IrElement.

^KT-65773 In Progress

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

@@ -38,6 +38,7 @@ val irTypeType = type(types, "IrType")
 val irFactoryType = type(declarations, "IrFactory")
 val stageControllerType = type(declarations, "StageController", TypeKind.Class)
 val idSignatureType = type(util, "IdSignature", TypeKind.Class)
+val irImplementationDetailType = type(tree, "IrImplementationDetail", TypeKind.Class)
 
 val symbolType = type(symbols, "IrSymbol")
 val packageFragmentSymbolType = type(symbols, "IrPackageFragmentSymbol")

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

@@ -100,7 +100,7 @@ object IrTree : AbstractTreeBuilder() {
     val declaration: Element by element(Declaration) {
         parent(statement)
         parent(symbolOwner)
-        parent(mutableAnnotationContainerType)
+        parent(mutableAnnotationContainer)
 
         +descriptor("DeclarationDescriptor")
         +field("origin", type(Packages.declarations, "IrDeclarationOrigin"))
@@ -323,6 +323,14 @@ object IrTree : AbstractTreeBuilder() {
             skipInIrFactory()
         }
     }
+    val mutableAnnotationContainer: Element by element(Declaration) {
+        parent(type(Packages.declarations, "IrAnnotationContainer"))
+
+        +listField("annotations", constructorCall, mutability = Var, isChild = false) {
+            fromParent = true
+            skipInIrFactory()
+        }
+    }
     val anonymousInitializer: Element by element(Declaration) {
         parent(declarationBase)