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.

routers/api/v1/repo/issue_reaction.go

@@ -175,7 +175,7 @@ func DeleteIssueCommentReaction(ctx *context.APIContext) {
 	//   schema:
 	//     "$ref": "#/definitions/EditReactionOption"
 	// responses:
-	//   "200":
+	//   "204":
 	//     "$ref": "#/responses/empty"
 	//   "403":
 	//     "$ref": "#/responses/forbidden"
@@ -248,8 +248,7 @@ func changeIssueCommentReaction(ctx *context.APIContext, form api.EditReactionOp
 			ctx.APIErrorInternal(err)
 			return
 		}
-		// ToDo respond 204
-		ctx.Status(http.StatusOK)
+		ctx.Status(http.StatusNoContent)
 	}
 }
 
@@ -408,7 +407,7 @@ func DeleteIssueReaction(ctx *context.APIContext) {
 	//   schema:
 	//     "$ref": "#/definitions/EditReactionOption"
 	// responses:
-	//   "200":
+	//   "204":
 	//     "$ref": "#/responses/empty"
 	//   "403":
 	//     "$ref": "#/responses/forbidden"
@@ -464,7 +463,6 @@ func changeIssueReaction(ctx *context.APIContext, form api.EditReactionOption, i
 			ctx.APIErrorInternal(err)
 			return
 		}
-		// ToDo respond 204
-		ctx.Status(http.StatusOK)
+		ctx.Status(http.StatusNoContent)
 	}
 }