Summary: Add Python bindings to the Rust progress wrappers. This may seem pointless since the Rust code just calls right back into Python, but this is a useful step to get the Rust and Python code to use a common interface for progress. (Which, in turn, will allow switching to a Rust progress implementation down the line.)
Reviewed By: markbt
Differential Revision: D23999816
fbshipit-source-id: 9bca0f23170d3ca474a1cb5d547840e63572ec71
