plug-ins: Migrate pipewire and remoting plug-ins headers to public header

directory

Weston is also a user of the plug-ins, so make use of it. With this change we unconditionally install the plug-in headers even though libweston might not be built with support for them.

Suggested-by: Pekka Paalanen pekka.paalanen@collabora.com Signed-off-by: Marius Vlad marius.vlad@collabora.com