Add logs for group child notification removal animation start and end

Add logs for group child notification removal animation process and end. For each "Group Child Notification removal event processed", there should be a corresponding "Group child notification removal animation ended" log, otherwise the removal animation of group child ends abruptly.

Bug: 281628358
Test: StackStateLoggerTest
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:b6c850554596c641084115af688f24992fcea45e)
Merged-In: I7fd2cb3a8d218908c5f2c2f9cd54d6a22b4f73d3
Change-Id: I7fd2cb3a8d218908c5f2c2f9cd54d6a22b4f73d3