Context Parallel SFT Support for dataset in THD format

[tomlifu]

What does this PR do ?

This PR adds CP support for THD format and is compatible with cu_seqlen_padded in the latest CUDNN fused attention.

PR Type:

• [x] New Feature
• [ ] Bugfix
• [ ] Documentation

If you haven't finished some of the above items you can still open "Draft" PR.