Improve IMF visibility log (1/N)

Add event log to record the show/hide IME
request InputMethodManagerService.

The log includes focused window, visibility
reason, soft input mode, and use the tag of
ImeTracker.Token for identification.

The log is only enabled for debug builds.

Bug: 239501597
Test: presubmit
Change-Id: I3b4d16ae441ce0628febfb6e18a54aae86cdab4a