Enable detectable autorepeat

Enable detectable autorepeat

https://www.x.org/releases/current/doc/kbproto/xkbproto.html#Detectable_Autorepeat

Detectable autorepeat should only affect --release bindings. Currently,
when a user keeps a key pressed, we get multiple KeyPress and KeyRelease
events. With this change, we still get multiple KeyPress events, which
means that you can still keep a key pressed to repeatedly execute a
normal binding, but only one KeyRelease event when the key is physically
released.

Unfortunately, this change is not currently testable because detectable
autorepeat doesn't seem to work under Xephyr. AwesomeWM experienced the
same problem:
https://github.com/awesomeWM/awesome/commit/6f2424e90170be4acaa1d140f966ab6bb8a4d217

Fixes #3306