[AutoDiff] Fix variedness propagation for `apply` inout arguments. (#28352)
Propagate variedness from `apply` argument operands to `apply` inout arguments
(representing results). `apply` inout arguments are now correctly marked as
active, triggering non-differentiability errors.
Add `ApplyInstBase::getInoutArguments` for iterating over `@inout` and
`@inout_aliasable` arguments.
Add non-differentiability diagnostics and activity info tests.
Resolves TF-974.