Revert "Revert "Expandable blocks in allocator (#96995)"" (#99275)
This reverts commit 851e89c8e817f28270e0fc21d74ced9446bea747.
Differential Revision: [D45034526](https://our.internmc.facebook.com/intern/diff/D45034526)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99275
Approved by: https://github.com/eellison
