onnxruntime

Allow sharing of initializers between sessions. (#5092)

* Allow sharing of initializers between sessions.

* Allow sharing of initializers between sessions (2).

* Add test for C#

* Add test for C#; address PR comments

* Address PR comments
Moved AddInitializer logic to internal session options
Added tests for owned buffer
Clarified documentation
Fix bug where memory info and not device was getting compared

* Fix test

* Fix training build

* Add ver 5 end marker and ver 6 starter, add scenario and usage examples.