libweston: Move 'struct weston_backend' to the internal backend header

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
2 jobs for libweston-split in 1 minute and 41 seconds (queued for 1 second)
Status Job ID Name Coverage
  Container Prep
passed #427064
container_prep

00:00:25

 
  Build
passed #427065
build-native-meson

00:01:16