Support DNN types in approximator

Mostly, it's relevant to FIR since there we started loading
type parameter based types as (T & Any..T?)

core/compiler.common/src/org/jetbrains/kotlin/types/model/TypeSystemContext.kt

@@ -584,6 +584,9 @@ interface TypeSystemContext : TypeSystemOptimizationContext {
 
     fun SimpleTypeMarker.asDefinitelyNotNullType(): DefinitelyNotNullTypeMarker?
     fun DefinitelyNotNullTypeMarker.original(): SimpleTypeMarker
+
+    fun SimpleTypeMarker.originalIfDefinitelyNotNullable(): SimpleTypeMarker = asDefinitelyNotNullType()?.original() ?: this
+
     fun KotlinTypeMarker.makeDefinitelyNotNullOrNotNull(): KotlinTypeMarker
     fun SimpleTypeMarker.makeSimpleTypeDefinitelyNotNullOrNotNull(): SimpleTypeMarker
     fun SimpleTypeMarker.isMarkedNullable(): Boolean