[Refactor] CombinedStatus and CommitStatus related functions & structs (#14026)

* RM unused struct

* rename (*CommitStatus) loadRepo() -> loadAttributes()

* move ToCommitStatus into its own file

* use CommitStatusState instead of StatusState

* move CombinedStatus convertion into convert package

* let models.GetLatestCommitStatus use repoID direct and accept ListOptions

* update swagger docs

* fix tests

* Fix swagger docs

* rm page

* fix swagger docs!!!

* return json null

* always return json

* rename api.Status to api.CommitStatus

* fix swagger docs

* sec swagger fix

routers/repo/commit.go

@@ -296,7 +296,7 @@ func Diff(ctx *context.Context) {
 		commitID = commit.ID.String()
 	}
 
-	statuses, err := models.GetLatestCommitStatus(ctx.Repo.Repository, commitID, 0)
+	statuses, err := models.GetLatestCommitStatus(ctx.Repo.Repository.ID, commitID, models.ListOptions{})
 	if err != nil {
 		log.Error("GetLatestCommitStatus: %v", err)
 	}