feat: Apply RoPE embedding with sequence offsets

[sudhakarsingh27]

What does this PR do ?

Allows applying rope embedding with "offsets" to sequences in packed (thd) or batch (bshd/sbhd) formats. The offset per sequence can be supplied as an argument start_positions tensor.

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flowchart LR
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[deepakn94]

/ok to test c3e83ad3c03c0de8771a2db7c2a66c23a1486f9f

[sudhakarsingh27]

/ok to test

[sudhakarsingh27]

/ok to test https://github.com/NVIDIA/Megatron-LM/pull/2416/commits/f0461ab06bf97267d25abf30b73686e31d3969f0