linux/x11: Reduce input latency and ensure rerender priority (#13355)

This change ensures that we always render a window according to its
refresh rate, even if there are a lot of X11 events.

We're working around some limitations of `calloop`. In the future, we
think we should revisit how the event loop is implemented on X11, so
that we can ensure proper prioritization of input events vs. rendering.

Release Notes:

- N/A

Co-authored-by: Antonio <me@as-cii.com>