grDevices::dev.capabilities() enhancements

[trevorld]

1. dev.capabilities() could also be used to query whether the current graphics device supports Unicode. In such a case I'd expect it to return FALSE if pdf() is the current graphics device and something else for the Cairo or Quartz devices.

   • https://stat.ethz.ch/pipermail/r-devel/2023-August/082845.html
   • A function that is my workaround for now

2. Add "Idle" as possible "event" in dev.capabilities("events"):

   • https://stat.ethz.ch/pipermail/r-devel/2022-April/081663.html
   • {eventloop} is an example package that needs to know the current graphics device supports the "Idle" event