fix cumsum and strided slice bugs

[pyu10055]

This address the issues we are seeing with the ddsp model.

1. cumsum the permutation logic is wrong, should to be able to reverse.
2. strided_slice has issue with ellipsis mask is set and end indexes has negative value.

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This change is 

[annxingyuan]

Thanks Ping!!!

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @annxingyuan)