add a minimal test for haxe.CallStack: check that callStack/exceptionStack always return an array at least

tests/unit/src/unitstd/haxe/CallStack.unit.hx

@@ -0,0 +1,5 @@
+var stack = haxe.CallStack.callStack();
+Std.is(stack, Array) == true;
+
+var stack = haxe.CallStack.exceptionStack();
+Std.is(stack, Array) == true;