Add missing rapidjson headers.

code/AssetLib/glTF2/glTF2Asset.inl

@@ -45,6 +45,9 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <assimp/StringUtils.h>
 #include <assimp/DefaultLogger.hpp>
 #include <assimp/Base64.hpp>
+#include <rapidjson/document.h>
+#include <rapidjson/schema.h>
+#include <rapidjson/stringbuffer.h>
 
 // clang-format off
 #ifdef ASSIMP_ENABLE_DRACO