messages: use proper multiline error message for rpcrequest and API wrappers

src/nvim/lua/executor.c

@@ -54,6 +54,7 @@ static void nlua_error(lua_State *const lstate, const char *const msg)
   size_t len;
   const char *const str = lua_tolstring(lstate, -1, &len);
 
+  msg_ext_set_kind("lua_error");
   emsgf_multiline(msg, (int)len, str);
 
   lua_pop(lstate, 1);