Introduce WITH_UNSIGNED directive to use unsigned types in tests

compiler/testData/codegen/box/inlineClasses/checkPlusOfUInt.kt

@@ -0,0 +1,11 @@
+// !LANGUAGE: +InlineClasses
+// !SKIP_METADATA_VERSION_CHECK
+// WITH_UNSIGNED
+
+@Suppress("INVISIBLE_MEMBER")
+fun box(): String {
+    val u1 = UInt(1)
+    val u2 = UInt(2)
+    val u3 = u1 + u2
+    return if (u3.toInt() == 3) "OK" else "fail"
+}