[LTC] Make even more LazyGraphExecutor interfaces virtual (#90650)
Summary:
This patch makes the following interfaces virtual for XLA to adopt:
1. LazyGraphExecutor::Async.
2. TensorCollectionBarrier
3. SyncLiveTensorsGraph
It's related to https://github.com/pytorch/xla/pull/4314.
Test Plan:
CI.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90650
Approved by: https://github.com/wconstab
