KT-13355: fix Kotlin compilation.

core/descriptors/src/org/jetbrains/kotlin/descriptors/TypeAliasDescriptor.kt

@@ -30,5 +30,7 @@ interface TypeAliasDescriptor : ClassifierDescriptorWithTypeParameters {
 
     val classDescriptor: ClassDescriptor?
 
+    override fun getOriginal(): TypeAliasDescriptor
+
     override fun substitute(substitutor: TypeSubstitutor): TypeAliasDescriptor
 }

core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/AbstractTypeAliasDescriptor.kt

@@ -76,6 +76,8 @@ abstract class AbstractTypeAliasDescriptor(
 
     override fun toString(): String = "typealias ${name.asString()}"
 
+    override fun getOriginal(): TypeAliasDescriptor = super.getOriginal() as TypeAliasDescriptor
+
     protected abstract fun getTypeConstructorTypeParameters(): List<TypeParameterDescriptor>
 
     protected fun computeDefaultType(): SimpleType =