Make ImeTrackerService onStart asynchronous

Currently the ImeTrackerService is mostly asynchronous, with the single
exception of the onStart, having all other updates come after it.

This modifies the service such that all calls are asynchronous, and
thus non-blocking binder calls. As the order of the calls is no longer
guaranteed, this requires handling cases where the first call is not
onStart, with the tracking of entries started in other calls as well.

Flag: EXEMPT refactor
Bug: 342111149
Test: atest ImeTrackerServiceTest
Change-Id: I9da6c3ecefb006d42e71a4e8aa3faac9e9223632