FIR: Fix incorrectly serialized type

See the test added: there's a non-denotable T!! type inside flexible type
that wasn't handled before.

ConeKotlinType::contains handles flexible types content and some other cases
Also, it has better asymptotics

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/types/TypeUtils.kt

@@ -11,7 +11,6 @@ import org.jetbrains.kotlin.fir.FirFakeSourceElementKind
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.declarations.classId
 import org.jetbrains.kotlin.fir.diagnostics.ConeSimpleDiagnostic
-import org.jetbrains.kotlin.fir.expressions.classId
 import org.jetbrains.kotlin.fir.fakeElement
 import org.jetbrains.kotlin.fir.render
 import org.jetbrains.kotlin.fir.resolve.fullyExpandedType
@@ -270,17 +269,8 @@ fun FirTypeRef.approximatedForPublicPosition(approximator: AbstractTypeApproxima
     else
         this
 
-private fun ConeKotlinType.requiresApproximationInPublicPosition(): Boolean {
-    return when (this) {
-        is ConeIntegerLiteralType,
-        is ConeCapturedType,
-        is ConeDefinitelyNotNullType,
-        is ConeIntersectionType -> true
-        is ConeClassLikeType -> typeArguments.any {
-            it is ConeKotlinTypeProjection && it.type.requiresApproximationInPublicPosition()
-        }
-        else -> false
-    }
+private fun ConeKotlinType.requiresApproximationInPublicPosition(): Boolean = contains {
+    it is ConeIntegerLiteralType || it is ConeCapturedType || it is ConeDefinitelyNotNullType || it is ConeIntersectionType
 }
 
 /*