Don't attach IME screenshot when performing non-task transition

As currently attaching IME screenshot is only valid during
switching between app tasks with IME window for aligning
with the IME window surface layer on the fullscreen activity.

The issue happens when SettingsPanelActivity (non-fullscreen activity)
launch another translucent activity and popup the wifi password dialog.

When user dismiss the dialog, it makes WifiDialogActivity
incidentally attachs the IME screenshot on SettingsPanelActivity
while performing translucent activity closing transition.

Since initially we only support IME screenshot when performing task
level app transition or switching apps with recents animation,

We won't support for the app activity with theming or popup the
non-fullscreen dialog with editor in case wrong IME screenshot
attaching as the above issue case during activity closing transition.

Add more checks to consolidate the attaching rule that valid only
when the task is IME layering target and performing task closing
transition.

Fix: 186080920
Test: atest DisplayContentTests#testAttachAndShowImeScreenshotOnTarget
Test: atest DisplayContentTests#testShowImeScreenshot
Test: manual as issue steps:
   1) Open Internet connection from quick settings.
   2) Choose a Wifi ssid which requires password.
   3) Enter password and press Enter key.
   4) Verify if the keyboard is still remain on the screen.
      Expected is not.
Change-Id: I0a0a8322c5d1cd44e3a4520c7f5434b8bc5b8306