internal/system: relocate from system

These packages are highly specific to hakurei and are difficult to use safely from other pieces of code.

Their exported symbols are made available until v0.4.0 where they will be removed for #24.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/system/wayland/wayland-client-helper.h

@@ -0,0 +1,4 @@
+#include <stdint.h>
+
+int32_t hakurei_bind_wayland_fd(char *socket_path, int fd, const char *app_id,
+                                const char *instance_id, int sync_fd);