Cleanup ATen-core forward declarations
I noticed that when `SymInt` was introduced, `jit_type_base.h` was
added as an include to the `Operator.h` template which is supposed to
be kept extremely clean and only use forward declarations. Also,
that forward declarations for `OptionalArrayRef` were missing.
So, I've refactored the forward declarations into
`ATen/core/ATen_fwd.h` and cleaned up some of the `c10`
headers that were masking these missing declarations. I've also
re-generated the pre-compiled header so `SymInt` is included.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76576
Approved by: https://github.com/albanD
