[Flow202][desktop][skip-ci] Fix Flow issues in desktop codebase
Summary:
This one was pretty simple... just added a bunch of types in various places.
NOTE: CI will fail on this diff. I considered the possibility of fixing Flow errors BEFORE upgrading Flow, but it wasn't possible... in some cases, the fixes to support the new version of Flow caused errors in the old version. I could have hidden these type errors with $FlowFixMe lines and then later revert those, but that seemed like too much busy work.
Test Plan: Make sure all Flow errors in desktop are resolved
Reviewers: michal
Reviewed By: michal
Subscribers: tomek, wyilio
Differential Revision: https://phab.comm.dev/D9721