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/testData/codegen/box/regressions/approximationForDefinitelyNotNull.kt

@@ -0,0 +1,57 @@
+// TARGET_BACKEND: JVM
+// WITH_RUNTIME
+
+// MODULE: lib
+// FILE: CachedValuesManager.java
+import org.jetbrains.annotations.NotNull;
+public class CachedValuesManager {
+    public @NotNull <T> CachedValue<T> createCachedValue(final @NotNull CachedValueProvider<T> provider) {
+        return new CachedValue<T>() {
+            public T getValue() {
+                return provider.compute().value;
+            }
+        };
+    }
+}
+
+// FILE: CachedValueProvider.java
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Collection;
+
+public interface CachedValueProvider<T> {
+    @Nullable
+    Result<T> compute();
+
+    class Result<T> {
+        public final T value;
+        public Result(@Nullable T value) {
+            this.value = value;
+        }
+    }
+}
+
+// FILE: CachedValue.java
+public interface CachedValue<T> {
+    T getValue();
+}
+
+// FILE: lib.kt
+
+// Inferred as CachedValue<ft<T!!, T>>! and T!! should be approximated
+fun <T> cachedValue(manager: CachedValuesManager, createValue: () -> T) =
+    manager.createCachedValue {
+        CachedValueProvider.Result(
+            createValue()
+        )
+    }
+
+// MODULE: main(lib)
+// FILE: main.kt
+
+fun box(): String {
+    val value = cachedValue(CachedValuesManager()) { Pair("O", "K") }.value
+
+    return value.first + value.second
+}