[ONNX] Update constant-folding of Gather op (#50554) (#51514)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51514
Update constant-folding of Gather operator so it also includes cases where rank of indices input is 0.
Currently it only support cases where rank of indices is 1.
Test Plan: Imported from OSS
Reviewed By: pbelevich
Differential Revision: D26191323
Pulled By: SplitInfinity
fbshipit-source-id: 7edcbd8835b0248fefb908aca394f5cca5eae29e
