MockIme: Use binder-based channel instead of broadcasts

- Replaces the command / event handlers with a RemoteCallback-based transport instead
  of relying on the broadcast queue. This helps avoid flakiness from the queue being
  under load from other things in the system
- Adds an unstableAcquireProvider reference to the MockIme to keep the process alive
- Removes the sticky broadcast mechanism, instead using the SettingsProvider to push
  autofill extras

Bug: 273796419
Test: atest CtsInputMethodTestCases
Change-Id: I642244e5e835adcb30c6671745a57155e473c764
6 files changed