Use expect_true to make split with unbacked sizes work. (#106788)
This pattern shows up in torchrec KeyedJaggedTensor. Most
of the change in this PR is mechanical: whenever we failed
an unbacked symint test due to just error checking, replace the
conditional with something that calls expect_true (e.g.,
torch._check or TORCH_SYM_CHECK).
Some of the changes are a bit more nuanced, I've commented on the PR
accordingly.
Signed-off-by: Edward Z. Yang <ezyang@meta.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106788
Approved by: https://github.com/lezcano
ghstack dependencies: #106720
