Add NUM_VALUES for enums and size for structs (see #3836)

API versioning requires that enumerations end with a count value
(`*_NUM_VALUES`) and structs begin with a size value (`size_t size`).
Wrapper templates are updated to support structs with different size
values indicating different versions.

To test:
Run `ceftests --gtest_filter=ApiVersionTest.StructVersion*`

libcef/browser/prefs/pref_registrar.cc

@@ -58,6 +58,9 @@ class CefPreferenceRegistrarImpl : public CefPreferenceRegistrar {
       case VTYPE_LIST:
         RegisterComplexPref(nameStr, default_value);
         return true;
+      case VTYPE_NUM_VALUES:
+        DCHECK(false);
+        return false;
     };
 
     LOG(ERROR) << "Invalid value type for preference: " << nameStr;