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>

pipewire/pipewire-plugin.c

@@ -822,11 +822,11 @@ weston_module_init(struct weston_compositor *compositor)
 		goto failed;
 	}
 
-	pipewire->debug = weston_compositor_add_log_scope(
-			compositor->weston_log_ctx,
-			"pipewire",
-			"Debug messages from pipewire plugin\n",
-			NULL, NULL, NULL);
+	pipewire->debug =
+		weston_log_ctx_add_log_scope(compositor->weston_log_ctx,
+					     "pipewire",
+					     "Debug messages from pipewire plugin\n",
+					     NULL, NULL, NULL);
 
 	return 0;