weston_compositor_add_log_scope() declaration is confusing

The declaration is

struct weston_log_scope *
weston_compositor_add_log_scope(struct weston_log_context *compositor,
                                  const char *name,
                                  const char *description,
                                  weston_log_scope_cb new_subscriber,
                                  void *user_data);

Problems:

• The function is named weston_compositor_... but it does not take a struct weston_compositor *.
• The first argument is of type struct weston_log_context * but named compositor.

I think we should have also a real weston_compositor_add_log_scope(struct weston_compositor *, ...) for the times when we already have a weston_compositor at hand. Accessing weston_compositor::weston_log_ctx in non-core code is a bit icky.