UnitTest: Add StringUtil ToString/TryParse test

Only a single one, but the main one for ini files:
Check if the written values can be parsed again.

Source/UnitTests/Common/StringUtilTest.cpp

@@ -84,3 +84,24 @@ TEST(StringUtil, UTF8ToSHIFTJIS)
   EXPECT_STREQ(SHIFTJISToUTF8(UTF8ToSHIFTJIS(kirby_unicode)).c_str(), kirby_unicode.c_str());
   EXPECT_STREQ(UTF8ToSHIFTJIS(kirby_unicode).c_str(), kirby_sjis.c_str());
 }
+
+template <typename T>
+static void DoRoundTripTest(const std::vector<T>& data)
+{
+  for (const T& e : data)
+  {
+    const std::string s = ValueToString(e);
+    T out;
+    EXPECT_TRUE(TryParse(s, &out));
+    EXPECT_EQ(e, out);
+  }
+}
+
+TEST(StringUtil, ToString_TryParse_Roundtrip)
+{
+  DoRoundTripTest<bool>({true, false});
+  DoRoundTripTest<int>({0, -1, 1, 123, -123, 123456789, -123456789});
+  DoRoundTripTest<unsigned int>({0u, 1u, 123u, 123456789u, 4023456789u});
+  DoRoundTripTest<float>({0.0f, 1.0f, -1.0f, -0.5f, 0.5f, -1e-3f, 1e-3f, 1e3f, -1e3f});
+  DoRoundTripTest<double>({0.0, 1.0, -1.0, -0.5, 0.5, -1e-3, 1e-3, 1e3, -1e3});
+}