Don't keep fixed orientation for multi-window task

Originally, only consider the non-top activty apply fixed orientation
if not in multi-window mode, it may still entering pip but not switched
multi-window mode, so add the check for parent task.

Bug: 419968658
Flag: EXEMPT bugfix
Test: m
1.Disable auto-rotate
2.Share the fullscreen landscape playing video from Youku to Wechat

Change-Id: I8182fd2fdd6c04534a09bf3a426e2aeda7e61d27