Move reaction to models/issues/ (#19264)

* Move reaction to models/issues/

* Fix test

* move the function

* improve code

* Update models/issues/reaction.go

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/container/map.go

@@ -0,0 +1,14 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package container
+
+// KeysInt64 returns keys slice for a map with int64 key
+func KeysInt64(m map[int64]struct{}) []int64 {
+	keys := make([]int64, 0, len(m))
+	for k := range m {
+		keys = append(keys, k)
+	}
+	return keys
+}