xwm: convert WM_DEBUG into a weston-debug scope

Instead of a compile time choice, offer the XWM debugging messages
through the weston-debug protocol and tool on demand. Users will not
need to recompile weston to get XWM debugging, and it won't flood the
weston log.

The debug scope needs to be initialized in launcher.c for it be
available from start, before the first X11 client tries to connect and
initializes XWM.

Signed-off-by: Pekka Paalanen <pq@iki.fi>

pass the wm_debug scope to weston_debug_scope_printf API to append
the scopename to the timestr

Signed-off-by: Maniraj Devadoss <Maniraj.Devadoss@in.bosch.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Daniel Stone <daniels@collabora.com>