The idea here is to track the cursor changes on the server side, ultimately [1] using a private message to notify user drivers of changes to apply, instead of tracking the changes in user drivers with throttle mechanisms.
This would greatly simplify winex11 mouse message handling as we would not need to try syncing the window cursor on every mouse move, and ultimately it would also make it possible to have a single thread listening to input in the background. Currently the input thread needs to own the windows that are under the cursor to be able to set it.
Having a single input thread (per-process at least, but ideally and ultimately per-prefix), will solve several issues with input not being received when the foreground thread isn't actively checking their message, as well as issues with DInput incorrectly checking window messages when it should not.
[1] See https://gitlab.winehq.org/rbernon/wine/-/merge_requests/8/commits