[FIR] support flexible types in ConeKotlinType#independentInstance

^KT-60580 Fixed

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java

@@ -20156,6 +20156,12 @@ public class FirLightTreeOldFrontendDiagnosticsTestGenerated extends AbstractFir
                 runTest("compiler/testData/diagnostics/tests/j+k/kt36856.kt");
             }
 
+            @Test
+            @TestMetadata("kt60580.kt")
+            public void testKt60580() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/j+k/kt60580.kt");
+            }
+
             @Test
             @TestMetadata("kt6720_abstractProperty.kt")
             public void testKt6720_abstractProperty() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java

@@ -20162,6 +20162,12 @@ public class FirPsiOldFrontendDiagnosticsTestGenerated extends AbstractFirPsiDia
                 runTest("compiler/testData/diagnostics/tests/j+k/kt36856.kt");
             }
 
+            @Test
+            @TestMetadata("kt60580.kt")
+            public void testKt60580() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/j+k/kt60580.kt");
+            }
+
             @Test
             @TestMetadata("kt6720_abstractProperty.kt")
             public void testKt6720_abstractProperty() throws Exception {

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

@@ -136,7 +136,22 @@ fun ConeDynamicType.Companion.create(session: FirSession): ConeDynamicType =
  *
  * @see CustomAnnotationTypeAttribute.independentInstance
  */
-fun ConeKotlinType.independentInstance(): ConeKotlinType = instanceWithIndependentArguments().instanceWithIndependentAnnotations()
+@OptIn(DynamicTypeConstructor::class)
+fun ConeKotlinType.independentInstance(): ConeKotlinType = if (this is ConeFlexibleType) {
+    val newLowerBound = lowerBound.independentInstance() as ConeSimpleKotlinType
+    val newUpperBound = upperBound.independentInstance() as ConeSimpleKotlinType
+    if (newLowerBound !== lowerBound || newUpperBound !== upperBound) {
+        when (this) {
+            is ConeRawType -> ConeRawType.create(newLowerBound, newUpperBound)
+            is ConeDynamicType -> ConeDynamicType(newLowerBound, newUpperBound)
+            else -> ConeFlexibleType(newLowerBound, newUpperBound)
+        }
+    } else {
+        this
+    }
+} else {
+    instanceWithIndependentArguments().instanceWithIndependentAnnotations()
+}
 
 private fun ConeKotlinType.instanceWithIndependentArguments(): ConeKotlinType {
     val typeProjections = typeArguments