generate CHECK_CAST for smartcasted 'this'

compiler/testData/codegen/box/typeInfo/implicitSmartCastedThis.kt

@@ -0,0 +1,13 @@
+open class A
+
+class B : A() {
+    fun foo(i: Int) = i
+}
+
+fun A.test() = if (this is B) foo(42) else 0
+
+fun box(): String {
+    if (B().test() != 42) return "fail1"
+    if (A().test() != 0) return "fail2"
+    return "OK"
+}

compiler/testData/codegen/box/typeInfo/smartCastedThis.kt

@@ -0,0 +1,11 @@
+package h
+
+open class A {
+    fun bar() = if (this is B) this.foo() else "fail"
+}
+
+class B() : A() {
+    fun foo() = "OK"
+}
+
+fun box() = B().bar()