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/main_test.go

@@ -7,7 +7,6 @@ package models
 import (
 	"testing"
 
-	issues_model "code.gitea.io/gitea/models/issues"
 	"code.gitea.io/gitea/models/organization"
 	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/models/unittest"
@@ -28,10 +27,6 @@ func TestFixturesAreConsistent(t *testing.T) {
 	unittest.CheckConsistencyFor(t,
 		&user_model.User{},
 		&repo_model.Repository{},
-		&Issue{},
-		&PullRequest{},
-		&issues_model.Milestone{},
-		&Label{},
 		&organization.Team{},
 		&Action{})
 }