Extract out inner classes from IMMS

InputMethodManagerService.java is still too long to read.

Let's extract out the following inner classes for better readability.

 * SoftInputShowHideHistory
 * StartInputHistory
 * StartInputInfo

This is a mechanical refacotring CL. There must be no observable
behavior change.

Fix: 328811026
Test: presubmit
Change-Id: I666fe7d3fae7090871a3496583dee30e7125b555