[LTC] Make DeviceContextArena protected (#90531)
Summary:
This patch makes DeviceContextArena protected such that XLAGraphExecutor can reuse it. In addition, it makes all methods that utilize DeviceContextArena virtual such that XLAGraphExecutor can override them to provide its own DeviceContextArena.
P.S. This patch depends on pytorch/xla#4307 too.
Test Plan:
CI.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90531
Approved by: https://github.com/antoniojkim, https://github.com/JackCaoG
