Optimize out trivial INSTANCEOF checks

#KT-18157 Fixed Target versions 1.1.4

compiler/testData/codegen/bytecodeText/nullCheckOptimization/trivialInstanceOf.kt

@@ -0,0 +1,24 @@
+sealed class A {
+    class B : A()
+
+    class C : A()
+}
+
+inline fun foo(): A = A.B()
+
+fun box(): String {
+    val a: A = foo()
+    val b: Boolean
+    when (a) {
+        is A.B -> b = true
+        is A.C -> b = false
+    }
+    return if (b) "OK" else "FAIL"
+}
+
+// 0 TABLESWITCH
+// 0 LOOKUPSWITCH
+// 0 ATHROW
+// 0 INSTANCEOF
+// 0 FAIL
+// 0 POP