[profiler] Allow record_function ctx manager to profile futures (#35055)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35055
This is the first step to improving the way RPCs are profiled as suggested by Ilia. For now, since RPC can return two different types of futures, we have to implement two different code paths, one for the python eager mode future and one for the jit future.
This diff implements the python eager part. We have defined a method `_call_end_callbacks_on_future` that takes in a future and schedules a `RecordFunction` to be completed as a callback on the future.
Once https://github.com/pytorch/pytorch/pull/35039 lands, we can implement the JIT codepath by registering an operator that takes a `Future(t)` as well.
These code paths will be merged once the futures are merged.
ghstack-source-id: 102478180
Test Plan: Added unit tests
Differential Revision: D20452003
fbshipit-source-id: 1acdcb073bd1f63d6fb2e78277ac0be00fd6671d
