[RESUBMIT] [pytorch] Migrating index_add cuda to ATen (#33548)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33548
Mostly just moved code.
Index dim and number of indices checks are added to make checks idential to index_add_cpu_
This is a resubmit of #30573, which got reverted.
Test Plan: Imported from OSS
Differential Revision: D20002248
Pulled By: gchanan
fbshipit-source-id: 46df4047cb3fc1dff37a15b83c70b2cbb7a6460b
