Fix lockscreen can't get IME insets when split-screen activated

As CL[1] fixed Keyboard covered input box after leaving split screen
with using getDefaultTaskDisplayArea().isSplitScreenModeActivated()
to check if needs to let IME window above the window when updating
the above insets state of windows, in case the windowing mode
configuration change not yet updated correctly during task reparenting.

However, this change will let notificationShade won't get IME insets
like when password lock shown, even split-screen is activated behind.

Since notificationShade is not the task window and shouldn't be affected
with splict-screen activivated checking, and we should exclude for
non-task window to ensure the shade can get IME insets.

[1]: I47bcb1234a49ea35c5e0d7281973fb3237e420eb

Fix: 188126678
Test: atest WindowStateTests#\
      testNotificationShadeHasImeInsetsWhenSplitscreenActivated
Test: manual as issue steps:
      1) Set password lock
      2) Active split screen with any 2 apps
      3) Lock phone then try to unlock
      4) Verify if password entry is visible and not covered by IME
Change-Id: Iff537bead93c977d19b820d6e64286a46f8e4982