Correct record activity snapshot condition.

Predictive back animation will happen when top activity has opt-in
enableOnBackInvokedCallback, and there will use activity snapshot for
previous activity.
So the correct condition is to record snapshot when opening activity
has opt-in onBackInvoked, instead of checking the closeing activity.

Bug: 259497289
Test: atest WindowOnBackInvokedDispatcherTest
Test: enable activity snapshot, and verify there will record activity
snapshot for close activity if the opening activity has opt-in
onBackInvoked.

Change-Id: I51814441bccd5e309cc3b310528b5c0bee3f24ba