patch 8.2.3961: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/json.c b/src/json.c
index a8d3a09..78a3a8e 100644
--- a/src/json.c
+++ b/src/json.c
@@ -933,7 +933,7 @@
 		top_item->jd_key = tv_get_string_buf_chk(cur_item, key_buf);
 		if (top_item->jd_key == NULL)
 		{
-		    emsg(_(e_invarg));
+		    emsg(_(e_invalid_argument));
 		    retval = FAIL;
 		    goto theend;
 		}
@@ -1164,7 +1164,7 @@
     reader.js_fill = NULL;
     reader.js_used = 0;
     if (json_decode_all(&reader, rettv, JSON_JS) != OK)
-	emsg(_(e_invarg));
+	emsg(_(e_invalid_argument));
 }
 
 /*