inplace PyTorchStreamReader getRecord() (#100418)
Summary: Sometimes we want to getRecord into an pre-allocated memory to save cpu memory. Adding new API to support the inplace memory writing.
Test Plan: caffe2/serialize/inline_container_test
Reviewed By: zyan0
Differential Revision: D45439517
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100418
Approved by: https://github.com/davidberard98, https://github.com/houseroad
