Allow only one -1 in nested view/reshape (#85691)
### this effectively means that we only allow reshaping/viewing of nt with ONE ragged dimension
Behavior before this PR:
1. `-1` allowed for implicit batch dimension
2. multiple `-1`s allowed for pre-existing dimensions
3. for new dimensions, `-1` is not allowed
it is worth noting that for the most part 3 is basically unreachable because assuming a nested tensor has at least 1 ragged dimension, you would expect at least one -1 to be in the proposed shape for the pre-existing dimensions
Behavior after this PR:
1. batch dimension **must be specified**
2. **only one** `-1` allowed for pre-existing dimensions **this effectively means that we only allow reshaping/viewing of nt with ONE ragged dimension**
3. unchanged
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85691
Approved by: https://github.com/cpuhrsch
