tests: add optional GoogleTest-based smoke-tests and CMake support (BUILD_GTEST_SMOKE)

Lts/DDS/DdsUnitTestsPlaceholder/ddsGenericDataTests_gtest.cpp

@@ -0,0 +1,13 @@
+#include <gtest/gtest.h>
+
+TEST(GenericSmokeGTest, BasicStringOps) {
+  std::string s = "MiXeD";
+  for (auto &c : s) c = (char)std::tolower(c);
+  EXPECT_EQ(s, "mixed");
+}
+
+TEST(GenericSmokeGTest, VariantLike) {
+  // simulate basic core logic check
+  int v = 42;
+  EXPECT_EQ(v + 1, 43);
+}