Introduce IInputMethodManager.InitParams

IInputMethod#initializeInternal() is a hot-spot where we keep adding
new parameters recently.  Introducing a dedicated parameter object
would allow us to add further parameters with fewer lines of changes.

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

Bug: 234882948
Test: presubmit
Change-Id: I98a5424385804ec190885ba53973935f9db66b88