TypeSystemContext: Rework raw types processing

All the current usages are about checking if the type is raw,
also in K2 it is simply incorrect to assume that only flexible types
might be raw

core/compiler.common.jvm/src/org/jetbrains/kotlin/load/java/typeEnhancement/AbstractSignatureParts.kt

@@ -204,7 +204,7 @@ abstract class AbstractSignatureParts<TAnnotation : Any> {
     private fun KotlinTypeMarker.toIndexed(): List<TypeAndDefaultQualifiers> = with(typeSystem) {
         TypeAndDefaultQualifiers(this@toIndexed, extractAndMergeDefaultQualifiers(containerDefaultTypeQualifiers), null).flattenTree {
             // Enhancement of raw type arguments may enter a loop in FE1.0.
-            if (skipRawTypeArguments && it.type?.asFlexibleType()?.asRawType() != null) return@flattenTree null
+            if (skipRawTypeArguments && it.type?.isRawType() == true) return@flattenTree null
 
             it.type?.typeConstructor()?.getParameters()?.zip(it.type.getArguments()) { parameter, arg ->
                 if (arg.isStarProjection()) {