Return all overloads for an operator in _jit_get_operation
This allows us to provide OpOverloadPacket.overloads method that
lists all of the overloads.
This isn't tested; will be exercised in the next PR.
Signed-off-by: Edward Z. Yang <ezyangfb.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76814
Approved by: https://github.com/mruberry
