Better isolate ResearchLogging data

Calls to LatinIME#onStartInputViewInternal log important information
about the context in which an IME is used.  This is reported as a
single LogStatement.  Previously, this was not placed into a separate
LogUnit, and was mixed in with general word data.  This change wraps
this LogStatement in its own LogUnit.

Change-Id: I0fecd41c8a1de622a764cc4b5d6902336697046c