Add vision transformer (#4077)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/4077

As titled. It will be useful for a few Cadence teams to be able to look at least at the AoT graph.

Reviewed By: dulinriley

Differential Revision: D59097944

fbshipit-source-id: ed94d5b1adfb9d26845062449127cee946e29092