NI: Prefer nullable lower bound to flexible one when substitution of type variable is performed and remember flexibility of type parameters based on flexibility of its upper bounds

^KT-32435 Fixed

js/js.tests/test/org/jetbrains/kotlin/js/test/ir/semantics/IrJsCodegenBoxTestGenerated.java

@@ -14256,6 +14256,11 @@ public class IrJsCodegenBoxTestGenerated extends AbstractIrJsCodegenBoxTest {
             KotlinTestUtils.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/codegen/box/platformTypes"), Pattern.compile("^(.+)\\.kt$"), null, TargetBackend.JS_IR, true);
         }
 
+        @TestMetadata("inferenceFlexibleTToNullable.kt")
+        public void testInferenceFlexibleTToNullable() throws Exception {
+            runTest("compiler/testData/codegen/box/platformTypes/inferenceFlexibleTToNullable.kt");
+        }
+
         @TestMetadata("compiler/testData/codegen/box/platformTypes/primitives")
         @TestDataPath("$PROJECT_ROOT")
         @RunWith(JUnit3RunnerWithInners.class)

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java

@@ -15436,6 +15436,11 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
             KotlinTestUtils.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/codegen/box/platformTypes"), Pattern.compile("^(.+)\\.kt$"), null, TargetBackend.JS, true);
         }
 
+        @TestMetadata("inferenceFlexibleTToNullable.kt")
+        public void testInferenceFlexibleTToNullable() throws Exception {
+            runTest("compiler/testData/codegen/box/platformTypes/inferenceFlexibleTToNullable.kt");
+        }
+
         @TestMetadata("compiler/testData/codegen/box/platformTypes/primitives")
         @TestDataPath("$PROJECT_ROOT")
         @RunWith(JUnit3RunnerWithInners.class)