获取最近任务

sequenceDiagram
ActivityManagerService ->> ActivityTaskManagerService: getRecentTasks
ActivityTaskManagerService ->> RecentTasks: getRecentTasks
RecentTasks ->> RecentTasks: loadUserRecentsLocked 
RecentTasks ->> RecentTasks: loadPersistedTaskIdsForUserLocked
RecentTasks ->> TaskPersister: restoreTasksForUserLocked

最近任务持久化存放目录/data/system_ce/0/recent_tasks