In issue comments, put issue participants also in completion list when hitting @ (#12433)

Previous behaviour was only to have completion for project members

templates/base/head.tmpl

@@ -78,12 +78,16 @@
 				EventSourceUpdateTime: {{NotificationSettings.EventSourceUpdateTime}},
 			},
       {{if .RequireTribute}}
-			tributeValues: [
+			tributeValues: Array.from(new Map([
+				{{ range .Participants }}
+				['{{.Name}}', {key: '{{.Name}} {{.FullName}}', value: '{{.Name}}',
+				name: '{{.Name}}', fullname: '{{.FullName}}', avatar: '{{.RelAvatarLink}}'}],
+				{{ end }}
 				{{ range .Assignees }}
-				{key: '{{.Name}} {{.FullName}}', value: '{{.Name}}',
-				name: '{{.Name}}', fullname: '{{.FullName}}', avatar: '{{.RelAvatarLink}}'},
+				['{{.Name}}', {key: '{{.Name}} {{.FullName}}', value: '{{.Name}}',
+				name: '{{.Name}}', fullname: '{{.FullName}}', avatar: '{{.RelAvatarLink}}'}],
 				{{ end }}
-			],
+			]).values()),
 			{{end}}
 		};
 	</script>