[blob] Implement cleanup helper functions
Summary:
Implementation of helpers introduced in D9350. These are part of the cleanup logic
and are extensively used in the next diff
Depends on D9350
Test Plan: The code compiles, these are tested thoroughly in the next diff
Reviewers: tomek, michal, varun, jon
Reviewed By: tomek, michal
Subscribers: ashoat, wyilio
Differential Revision: https://phab.comm.dev/D9351