KJT custom op for 1d lengths input

[TroyGarden]

Summary: X-link: https://github.com/pytorch/FBGEMM/pull/2774

context

• move the tensor.view(-1, stride) from python into the operator (c++)
• make the PT2 complier happy
• reference: D58948987

notes

• not sure if we should directly change the op call in the jagged_tensor
• tested in CPU
• backward and GPU haven't tested

Differential Revision: D58956327

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D58956327

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D58956327