functionalization: fix detach() (#87750)
`.detach()` worked in basic cases previously, but didn't properly preserve view relationships between the base and the output. This wasn't heavily tested, because autograd doesn't normally encounter `FunctionalTensorWrapper` directly, but could become more common if we fuse functionalization and autograd into a single tracing pass.
This will also be a bug fix for LTC (and XLA when they use functionalization)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87750
Approved by: https://github.com/ezyang
