No warning/info log for expected/normal situations

This CL hides warning and info log messages from
InputMethodManagerService (IMMS) and InputMethodService (IMS) behind
DEBUG flag like other logs unless the state is certainly unusual.

Of course the definition of "unusual" is still an open question, but
basically that we should not see any suspicious message from IMMS/IMS
just by turning on a new phone, launching some applications, typing
something, and turning off the device. IMMS and IMS should expect all
events that can (easily) occur in that scenario, and no log is
necessary for such things.

Note that warnings suppressed with TODO comments will be tracked
under Bug 34851776 (and Bug 34886274).

Test: adb logcat -s InputMethodManagerService:* InputMethodService:*
      to monitor log in the following scenario:
       1. Boot the device.
       2. Complete the setup wizard.
       3. Launch Dialer and type something on it.
       4. Launch Contacts app and type something on it.
       5. Try some special modes:
           - Turn on/off display
           - Recents screen
           - Split-window mode
           - Guest user
           - Multi user
           - Direct-boot (setup a device password and reboot)
      except for logs about actual IPC calls from a background user.
Bug: 34838583
Bug: 34851776
Bug: 34886274
Change-Id: I3fcdeb919bb2f2940da9ff45e17ac00baa1253f4