Expose setNumThreads to android api (#31033)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31033
Intention:
There are requests from users to control number of threads from android side:
https://discuss.pytorch.org/t/android-pytorch-forward-method-running-in-a-separate-thread-slow-down-ui-thread/63516/2
https://discuss.pytorch.org/t/threading-of-model-pytorch-android/62490/2
At the moment `setNumThreads` is placed in `org.pytorch.Module`, but this method changes global threadPool size, in future we will move it to some separate class to repeat python binding structure, which has torch.set_num_threads()
Test Plan: Imported from OSS
Differential Revision: D18923167
Pulled By: IvanKobzarev
fbshipit-source-id: 8d98c2edbff42e9b673509672dce3f2dd03a923e
