[FIR] Unwrap dispatcher type when determining property stability

If the modality of a property is not final, the modality of the dispatch
receiver can be used to determine if the property is stable. When
looking up the dispatch receiver symbol, make sure to unwrap the lower
bounds of flexible types.

^KT-61735 Fixed

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

@@ -26058,6 +26058,12 @@ public class FirLightTreeOldFrontendDiagnosticsTestGenerated extends AbstractFir
                 runTest("compiler/testData/diagnostics/tests/properties/extensionPropertyMustHaveAccessorsOrBeAbstract.kt");
             }
 
+            @Test
+            @TestMetadata("flexibleTypeReceiver.kt")
+            public void testFlexibleTypeReceiver() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/properties/flexibleTypeReceiver.kt");
+            }
+
             @Test
             @TestMetadata("inferPropertyTypeFromGetter.kt")
             public void testInferPropertyTypeFromGetter() throws Exception {

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

@@ -26064,6 +26064,12 @@ public class FirPsiOldFrontendDiagnosticsTestGenerated extends AbstractFirPsiDia
                 runTest("compiler/testData/diagnostics/tests/properties/extensionPropertyMustHaveAccessorsOrBeAbstract.kt");
             }
 
+            @Test
+            @TestMetadata("flexibleTypeReceiver.kt")
+            public void testFlexibleTypeReceiver() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/properties/flexibleTypeReceiver.kt");
+            }
+
             @Test
             @TestMetadata("inferPropertyTypeFromGetter.kt")
             public void testInferPropertyTypeFromGetter() throws Exception {