Update 'this' extension receiver when there's a smart cast

If 'this' (implicit or explicit) was used as an extension receiver,
and the corresponding call required a smart-cast,
this information was effectively lost in "old" resolution & inference,
but is required by "old" JVM BE to generate proper CHECKCASTs.

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java

@@ -17600,6 +17600,18 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             doTest(fileName);
         }
 
+        @TestMetadata("kt19058.kt")
+        public void testKt19058() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/smartCasts/kt19058.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("kt19100.kt")
+        public void testKt19100() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/smartCasts/kt19100.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("lambdaArgumentWithoutType.kt")
         public void testLambdaArgumentWithoutType() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/smartCasts/lambdaArgumentWithoutType.kt");