Merge more symbolic meta kernels and symint changes from branch (#86334)
symintify split_with_sizes, dropout, fused_fake_obs_quant. meta for padding_2d ops
add meta_bernoulli_
meta kernel for at::gather
get pytorch_struct to pass: meta for scatter_add, fix backward
symintify split ops
Pull Request resolved: https://github.com/pytorch/pytorch/pull/86334
Approved by: https://github.com/ezyang
