Adding Gradient Accumulation Data Type Config (#2512)
* Adding gradient accumulation dtype config.
* Switching to new DtypeEnum
* Adding standalone check function, and unit tests
* Variable disambiguation
* Adding checks for unsupported states.
* Updating for PR comments.
* Reorganizing unit test.
Co-authored-by: Olatunji Ruwase <olruwase@microsoft.com>
