Start tracking IME user animation requests

This starts tracking IME user animation requests again. These were
temporarily stopped as they required adding the onStart call on the UI
thread call path, which triggered a jank regression.

Now that ImeTracker onStart is also asynchronous, we can start tracking
these types of requests again.

This is essentially a revert of [1].

  [1]: I251edecfd4d26d3bed90448a6062ccd029bbd0ed

Flag: EXEMPT bugfix
Test: enable Swipe up to start search, trigger user animation in all
  apps, observe logcat
Bug: 342111149
Change-Id: Ic35bf71c084fadd291cb6964156f2d6c7ceed63a