Introduce InputMethodServiceInternal for better abstraction

This is a mechanical refactoring CL that has no behavior change.

This CL removes the direct dependency on AbstractInputMethodService
from whenever possible.  As a result, the following classes no longer
directly depend on AbstractInputMethodService.

 * android.inputmethodservice.IInputMethodWrapper
 * android.inputmethodservice.RemoteInputConnection
 * com.android.internal.inputmethod.ImeTracing
 * com.android.internal.inputmethod.ImeTracingClientImpl
 * com.android.internal.inputmethod.ImeTracingServerImpl

This is still a purely mechanical refactoring.  There should be no
observable behavior change.

Bug: 192412909
Test: atest CtsInputMethodTestCases
Test: Manually verified that IME tracing still works
Change-Id: I2aeeeacd27195ce10059d6590e098a4a969e774d