Fix IME snapshot applied on non-IME input target window

In case when the activity shows IME, transitioning from non-IME input
targeted dialog activity will see a weird IME snapshot sliding down
animation during the dialog dismissing.

Also added a flicker test to verify this behavior.

Fix: 210868010
Test: manual as below steps:
   1) Launch keep note app
   2) Tap on any url link to popup "open with" dialog
   3) Tap anywhere else on the screen to dismiss the dialog
   4) Expect no IME sliding down animation
Test: atest LaunchAppShowImeAndDialogThemeAppTest
Test: atest DisplayContentTests#testAttachAndShowImeScreenshotOnTarget

Change-Id: Ibccaea46547e57b3439c5e787f97a261fbb10125