Move issues related files into models/issues (#19931)

* Move access and repo permission to models/perm/access

* fix test

* fix git test

* Move functions sequence

* Some improvements per @KN4CK3R and @delvh

* Move issues related code to models/issues

* Move some issues related sub package

* Merge

* Fix test

* Fix test

* Fix test

* Fix test

* Rename some files

models/issues/issue_index.go

@@ -0,0 +1,32 @@
+// Copyright 2017 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 issues
+
+import "code.gitea.io/gitea/models/db"
+
+// RecalculateIssueIndexForRepo create issue_index for repo if not exist and
+// update it based on highest index of existing issues assigned to a repo
+func RecalculateIssueIndexForRepo(repoID int64) error {
+	ctx, committer, err := db.TxContext()
+	if err != nil {
+		return err
+	}
+	defer committer.Close()
+
+	if err := db.UpsertResourceIndex(ctx, "issue_index", repoID); err != nil {
+		return err
+	}
+
+	var max int64
+	if _, err := db.GetEngine(ctx).Select(" MAX(`index`)").Table("issue").Where("repo_id=?", repoID).Get(&max); err != nil {
+		return err
+	}
+
+	if _, err := db.GetEngine(ctx).Exec("UPDATE `issue_index` SET max_index=? WHERE group_id=?", max, repoID); err != nil {
+		return err
+	}
+
+	return committer.Commit()
+}