weston-log: rename the confusing function name weston_compositor_add_log_scope()

There's a function named weston_compositor_add_log_scope()
but it doesn't take a struct weston_compositor argument.

Rename it to weston_log_ctx_add_log_scope(), as
the log_scope is being added to a log_context.

Also, bump libweston_major to 9.

Signed-off-by: Leandro Ribeiro <leandrohr@riseup.net>

include/libweston/weston-log.h

@@ -55,7 +55,7 @@ struct weston_debug_stream;
  *
  * @param sub The subscription.
  * @param user_data The \c user_data argument given to
- * weston_compositor_add_log_scope()
+ * weston_log_ctx_add_log_scope()
  *
  * @memberof weston_log_scope
  */
@@ -63,12 +63,12 @@ typedef void (*weston_log_scope_cb)(struct weston_log_subscription *sub,
 				    void *user_data);
 
 struct weston_log_scope *
-weston_compositor_add_log_scope(struct weston_log_context *log_ctx,
-				  const char *name,
-				  const char *description,
-				  weston_log_scope_cb new_subscription,
-				  weston_log_scope_cb destroy_subscription,
-				  void *user_data);
+weston_log_ctx_add_log_scope(struct weston_log_context *log_ctx,
+			     const char *name,
+			     const char *description,
+			     weston_log_scope_cb new_subscription,
+			     weston_log_scope_cb destroy_subscription,
+			     void *user_data);
 
 void
 weston_compositor_log_scope_destroy(struct weston_log_scope *scope);