Move some tests from boxWithStdlib/ to box/

Move those tests which do not require neither stdlib nor reflect

compiler/testData/codegen/box/increment/extOnLong.kt

@@ -0,0 +1,8 @@
+operator fun Long.get(i: Int) = this
+operator fun Long.set(i: Int, newValue: Long) {}
+
+fun box(): String {
+    var x = 0L
+    val y = x[0]++
+    return if (y == 0L) "OK" else "Failed, y=$y"
+}