main: Move MetaCompositorType to a new meta-enums.h

It'll be part of and owned by MetaContext, intending to replace
`meta_is_wayland_compositor()`, but place it in a new file for public
enums so that it can be used from wherever.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1861>

src/core/main-private.h

@@ -21,14 +21,7 @@
 #define META_MAIN_PRIVATE_H
 
 #include "core/util-private.h"
-
-typedef enum _MetaCompositorType
-{
-#ifdef HAVE_WAYLAND
-  META_COMPOSITOR_TYPE_WAYLAND,
-#endif
-  META_COMPOSITOR_TYPE_X11,
-} MetaCompositorType;
+#include "meta/meta-enums.h"
 
 typedef enum _MetaX11DisplayPolicy
 {

src/core/main.c

@@ -83,6 +83,7 @@
 #include "core/util-private.h"
 #include "meta/compositor.h"
 #include "meta/meta-backend.h"
+#include "meta/meta-enums.h"
 #include "meta/meta-x11-errors.h"
 #include "ui/ui.h"
 #include "x11/session.h"

src/core/mutter.c

@@ -25,6 +25,7 @@
 
 #include "compositor/meta-plugin-manager.h"
 #include "meta/main.h"
+#include "meta/meta-enums.h"
 #include "meta/util.h"
 
 static gboolean