Originally contributed as #9603
I ended up coming back to this since it seems like a reasonable way to migrate
users in the short-medium term. We'll remove this in a later release.
Co-authored-by: Shamicen <Shamicen@users.noreply.github.com>
These are basically 1-to-1 replacements for the existing RxJava APIs.
This will make the initial migration off of RxJava simpler. We'll
revisit the actual call flows in followup versions of the API.
