K2: Fix false-positive UNSAFE_CALL on safe call with flexible type alias

The idea of the fix is just unwrapping flexible version of type alias,
before creating a not-nullable version for safe-call subject.

Otherwise, it was remained to be JsExpressionResult after applying
makeConeTypeDefinitelyNotNullOrNotNull (and the type is still nullable)

^KT-57190 Fixed

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java

@@ -27811,6 +27811,22 @@ public class DiagnosisCompilerTestFE10TestdataTestGenerated extends AbstractDiag
             }
         }
 
+        @Nested
+        @TestMetadata("compiler/testData/diagnostics/tests/safeCalls")
+        @TestDataPath("$PROJECT_ROOT")
+        public class SafeCalls {
+            @Test
+            public void testAllFilesPresentInSafeCalls() throws Exception {
+                KtTestUtil.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/diagnostics/tests/safeCalls"), Pattern.compile("^(.+)\\.kt$"), Pattern.compile("^(.+)\\.(fir|ll)\\.kts?$"), true);
+            }
+
+            @Test
+            @TestMetadata("safeCallOnFlexibleTypeAlias.kt")
+            public void testSafeCallOnFlexibleTypeAlias() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/safeCalls/safeCallOnFlexibleTypeAlias.kt");
+            }
+        }
+
         @Nested
         @TestMetadata("compiler/testData/diagnostics/tests/samConversions")
         @TestDataPath("$PROJECT_ROOT")