Add reflection support for python (#7026)

We already have the reflection.fbs file and the flatbuffers
python language support.

Adding this feature would give the python developers the
ability to parse the flatbuffers schema and write some tools.

Co-authored-by: Derek Bailey <derekbailey@google.com>

python/flatbuffers/reflection/AdvancedFeatures.py

@@ -0,0 +1,10 @@
+# automatically generated by the FlatBuffers compiler, do not modify
+
+# namespace: reflection
+
+# New schema language features that are not supported by old code generators.
+class AdvancedFeatures(object):
+    AdvancedArrayFeatures = 1
+    AdvancedUnionFeatures = 2
+    OptionalScalars = 4
+    DefaultVectorsAndStrings = 8