[deploy] loader cleanup (#62223)
Summary:
Some refactoring of the custom loader logic:
* Make sure we unregister frames when they are deleted so that future exceptions do not attempt to read unallocated memory
* rename linker -> loader to make its name more correct
* move the build of the loader into lib deploy since it can be shared across interpreters
* unify the logic for finding the library symbol across ops and fbcode
Pull Request resolved: https://github.com/pytorch/pytorch/pull/62223
Test Plan: Imported from OSS
Reviewed By: wconstab
Differential Revision: D29922002
Pulled By: zdevito
fbshipit-source-id: b7f8ee5812e29a5d098fcf1bd9f4cea7d30ecb4c
