Keeping consistent between UI and API about combined commit status state and fix some bugs (#34562)

Extract from #34531 

## Move Commit status state to a standalone package

Move the state from `structs` to `commitstatus` package. It also
introduce `CommitStatusStates` so that the combine function could be
used from UI and API logic.

## Combined commit status Changed

This PR will follow Github's combined commit status. Before this PR,
every commit status could be a combined one.
According to
https://docs.github.com/en/rest/commits/statuses?apiVersion=2022-11-28#get-the-combined-status-for-a-specific-reference
> Additionally, a combined state is returned. The state is one of:
> failure if any of the contexts report as error or failure
> pending if there are no statuses or a context is pending
> success if the latest status for all contexts is success

This PR will follow that rule and remove the `NoBetterThan` logic. This
also fixes the inconsistent between UI and API. In the API convert
package, it has implemented this which is different from the UI. It also
fixed the missing `URL` and `CommitURL` in the API.

## `CalcCommitStatus` return nil if there is no commit statuses

The behavior of `CalcCommitStatus` is changed. If the parameter commit
statuses is empty, it will return nil. The reference places should check
the returned value themselves.

1 files changed, 6 insertions, 6 deletions

diff --git a/models/git/commit_status_summary.go b/models/git/commit_status_summary.go
index 774e49bb98..dd416fa015 100644
--- a/models/git/commit_status_summary.go
+++ b/models/git/commit_status_summary.go
@@ -7,19 +7,19 @@ import (
 	"context"
 
 	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/modules/commitstatus"
 	"code.gitea.io/gitea/modules/setting"
-	api "code.gitea.io/gitea/modules/structs"
 
 	"xorm.io/builder"
 )
 
 // CommitStatusSummary holds the latest commit Status of a single Commit
 type CommitStatusSummary struct {
-	ID        int64                 `xorm:"pk autoincr"`
-	RepoID    int64                 `xorm:"INDEX UNIQUE(repo_id_sha)"`
-	SHA       string                `xorm:"VARCHAR(64) NOT NULL INDEX UNIQUE(repo_id_sha)"`
-	State     api.CommitStatusState `xorm:"VARCHAR(7) NOT NULL"`
-	TargetURL string                `xorm:"TEXT"`
+	ID        int64                          `xorm:"pk autoincr"`
+	RepoID    int64                          `xorm:"INDEX UNIQUE(repo_id_sha)"`
+	SHA       string                         `xorm:"VARCHAR(64) NOT NULL INDEX UNIQUE(repo_id_sha)"`
+	State     commitstatus.CommitStatusState `xorm:"VARCHAR(7) NOT NULL"`
+	TargetURL string                         `xorm:"TEXT"`
 }
 
 func init() {