Add advance feature indicators to reflection (#6546)

* Add advance feature indicators to reflection

* deserialize too

* model advanced features as bitflags

* use uint64_t instead of AdvancedFeatures

* git clang format

* initialize advanced_features_

* remove whitespace

Co-authored-by: Casper Neo <cneo@google.com>

include/flatbuffers/idl.h

@@ -780,6 +780,7 @@ class Parser : public ParserState {
         root_struct_def_(nullptr),
         opts(options),
         uses_flexbuffers_(false),
+        advanced_features_(0),
         source_(nullptr),
         anonymous_counter_(0),
         parse_depth_counter_(0) {
@@ -1011,6 +1012,8 @@ class Parser : public ParserState {
   IDLOptions opts;
   bool uses_flexbuffers_;
 
+  uint64_t advanced_features_;
+
  private:
   const char *source_;