xserver/output: rename some badly named variables/APIs.

This is an API and ABI break

Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
4 jobs for fix-randr-variable-naming in 6 minutes and 50 seconds (queued for 1 second)
Status Job ID Name Coverage
  Docker Image
passed #3536285
debian-testing

00:00:18

 
  Build And Test
passed #3536286
autotools

00:06:31

passed #3536287
meson

00:02:25

passed #3536288
meson-noglamor

00:02:18