RESTRICT AUTOMERGE: Fix snapshot starting window stuck if the task never gain focus

The tasksnapshot starting window could stuck on task if the task never
gain focus, this could happen when launch multiple tasks to front, e.g.
split screen, or add snapshot starting window to a pip task.

As using task focus to judge the task snapshot removal may error-prone.
(i.e. unexpected window focus in/lost, non-focusable task window..)

To ensure the tasksnapshot removal works stable in this stage, extanding
MAX_DELAY_REMOVAL_TIME_IME_VISIBLE timeout from 450ms to 600ms
(Includes the worst time perviod from tasksnapshot drawn to the task window
focused around 150ms) would be safer and keeps the behavior of original
fixed Bug 192065018.

Bug: 201264769
Test: atest ActivityRecordTests
Test: manual launch apps from Recents.
Test: enter pip, power on/off, verify starting window is removed.
Test: manual enter split screen, verify starting window is removed.
Merged-In: Ieb5a5e781f5da4228cfc493031b4ad17f2d31a77
Change-Id: Ieb5a5e781f5da4228cfc493031b4ad17f2d31a77