Magnification: Fix screen freeze after activity resumes from rotation

mMagnifedViewport.onRotationChangedLocked() will call setShown(),
and then cancel a anime. As the anime should be only canceled in
a looper, if it is executed in the onRotationChangedLocked() of
DisplayMagnifier, a crash will be caused. Therefore when the
magnification is enabled, the activity will crash after rotation.

Move mMagnifedViewport.onRotationChangedLocked() from main thread
into the handler. When MESSAGE_NOTIFY_ROTATION_CHANGED is received,
execute it. As handler is created with a looper, the crash will be
fixed.

CRs-Fixed: 541799

Change-Id: I2a78f24f73d5a9b8693e557d18e2fb01fcaec8fa