protocol: add weston-debug.xml

This is a new debugging extension for non-production environments. The
aim is to replace all build-time choosable debug prints in the
compositor with runtime subscribable debug streams.

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

Added new libweston-$MAJOR-protocols.pc file and install that
for external projects to find the XML files installed by libweston.

Signed-off-by: Maniraj Devadoss <Maniraj.Devadoss@in.bosch.com>
[Pekka: use noarch_pkgconfig_DATA instead, add ${pc_sysrootdir}]
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>