Correct swagger annotations for enums, status codes, and notification state (#37030)

## ⚠️ BREAKING ⚠️

- delete reaction endpoints is changed to return 204 No Content rather
than 200 with no content.

## Summary

Add swagger:enum annotations and migrate all enum comments from the
deprecated comma-separated format to JSON arrays. Introduce
NotifySubjectStateType with open/closed/merged values. Fix delete
reaction endpoints to return 204 instead of 200.

modules/structs/notifications.go

@@ -40,7 +40,7 @@ type NotificationSubject struct {
 	// Type indicates the type of the notification subject
 	Type NotifySubjectType `json:"type" binding:"In(Issue,Pull,Commit,Repository)"`
 	// State indicates the current state of the notification subject
-	State StateType `json:"state"`
+	State NotifySubjectStateType `json:"state"`
 }
 
 // NotificationCount number of unread notifications
@@ -49,7 +49,22 @@ type NotificationCount struct {
 	New int64 `json:"new"`
 }
 
+// NotifySubjectStateType represents the state of a notification subject
+// swagger:enum NotifySubjectStateType
+type NotifySubjectStateType string
+
+const (
+	// NotifySubjectStateOpen is an open subject
+	NotifySubjectStateOpen NotifySubjectStateType = "open"
+	// NotifySubjectStateClosed is a closed subject
+	NotifySubjectStateClosed NotifySubjectStateType = "closed"
+	// NotifySubjectStateMerged is a merged pull request
+	NotifySubjectStateMerged NotifySubjectStateType = "merged"
+)
+
 // NotifySubjectType represent type of notification subject
+//
+// swagger:enum NotifySubjectType
 type NotifySubjectType string
 
 const (