[IR generator] Inherit Field from AbstractField

This is a step towards commonizing the code generator between
FIR and IR: KT-61970

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/model/Field.kt

@@ -35,6 +35,16 @@ sealed class Field : AbstractField() {
 
     var withBindThis = true
 
+    abstract override var isVolatile: Boolean
+
+    abstract override var isFinal: Boolean
+
+    abstract override var isLateinit: Boolean
+
+    abstract override var isParameter: Boolean
+
+    abstract override var isMutable: Boolean
+
     override fun getTypeWithArguments(notNull: Boolean): String = type + generics + if (nullable && !notNull) "?" else ""
 
     fun copy(): Field = internalCopy().also {