Simplistic Calculator (#1030)

* Simplistic Calculator, initial commit

* Add Linux runner

* Add macOS runner, update `main.dart` for iOS

* Add a test

simplistic_calculator/linux/main.cc

@@ -0,0 +1,6 @@
+#include "my_application.h"
+
+int main(int argc, char** argv) {
+  g_autoptr(MyApplication) app = my_application_new();
+  return g_application_run(G_APPLICATION(app), argc, argv);
+}