Extend the test of MonsterExtra (#5428)

* Extend the test of MonsterExtra

- Extend C++ test of MonsterExtra
- Add conversion of fbs/json NaNs to unsigned quiet-NaN
- Update documentation (cross-platform interoperability)

* Fix declaration of infinity constants int the test

tests/monsterdata_extra.json

@@ -1,11 +1,15 @@
 {
-  // Float-point values with NaN and Inf defaults.
-  testf_nan : nan,
-  testf_pinf : +inf,
-  testf_ninf : -inf,
-  testd_nan  : nan,
-  testd_pinf : +inf,
-  testd_ninf : -inf,
-  testf_vec : [-1.0, 2.0, -inf, +inf, nan],
-  testd_vec : [-1.0, 4.0, -inf, +inf, nan]
+  // Initialize with non-default values.
+  d0 : -nan, // match with default
+  d1 : +inf,
+  d2 : -inf,
+  d3:   nan,
+  f0 : +nan, // match with default
+  f1 : -nan, // match with default
+  f2 : +inf, // match with default
+  f3 : -inf, // match with default
+  // Values should have exact binary representation 
+  // to avoid rounding effects in tests.
+  dvec : [2.0, +inf, -inf, nan,],
+  fvec : [1.0, -inf, +inf, nan],
 }