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>

compositor/main.c

@@ -3162,7 +3162,7 @@ wet_main(int argc, char *argv[])
 		return EXIT_FAILURE;
 	}
 
-	log_scope = weston_compositor_add_log_scope(log_ctx, "log",
+	log_scope = weston_log_ctx_add_log_scope(log_ctx, "log",
 			"Weston and Wayland log\n", NULL, NULL, NULL);
 
 	weston_log_file_open(log);
@@ -3248,10 +3248,9 @@ wet_main(int argc, char *argv[])
 	segv_compositor = wet.compositor;
 
 	protocol_scope =
-		weston_compositor_add_log_scope(log_ctx,
-						"proto",
-						"Wayland protocol dump for all clients.\n",
-						 NULL, NULL, NULL);
+		weston_log_ctx_add_log_scope(log_ctx, "proto",
+					     "Wayland protocol dump for all clients.\n",
+					     NULL, NULL, NULL);
 
 	protologger = wl_display_add_protocol_logger(display,
 						     protocol_log_fn,