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

compiler/resolution.common/src/org/jetbrains/kotlin/types/AbstractTypeApproximator.kt

@@ -118,7 +118,7 @@ abstract class AbstractTypeApproximator(
             is FlexibleTypeMarker -> {
                 if (type.isDynamic()) {
                     return if (conf.dynamic) null else type.bound()
-                } else if (type.asRawType() != null) {
+                } else if (type.isRawType()) {
                     return if (conf.rawType) null else type.bound()
                 }