Merge boxWithStdlib testData into box, delete BoxWithStdlib test

compiler/testData/codegen/box/boxingOptimization/checkcastAndInstanceOf.kt

@@ -0,0 +1,23 @@
+// WITH_RUNTIME
+
+import kotlin.test.assertEquals
+
+inline fun <R, T> foo(x : R, y : R, block : (R) -> T) : T {
+    val a = x is Number
+    val b = x is Object
+
+    val b1 = x as Object
+
+    if (a && b) {
+        return block(x)
+    } else {
+        return block(y)
+    }
+}
+
+fun box() : String {
+    assertEquals(1, foo(1, 2) { x -> x as Int })
+    assertEquals("def", foo("abc", "def") { x -> x as String })
+
+    return "OK"
+}