patch 8.2.1281: the "trailing characters" error can be hard to understand

Problem:    The "trailing characters" error can be hard to understand.
Solution:   Add the trailing characters to the message.
diff --git a/src/json.c b/src/json.c
index c22864d..8262640 100644
--- a/src/json.c
+++ b/src/json.c
@@ -1086,7 +1086,7 @@
     json_skip_white(reader);
     if (reader->js_buf[reader->js_used] != NUL)
     {
-	emsg(_(e_trailing));
+	semsg(_(e_trailing_arg), reader->js_buf + reader->js_used);
 	return FAIL;
     }
     return OK;