Merge inputmethodcommon into LatinIME repo

This is a preparation to deprecate frameworks/opt/inputmethodcommon
repository.

Currently repository 'inputmethodcommon' is used only from LatinIME.
Having such a repository only for one project is overkill.  Also, to
add gradle build support to LatinIME project, it would be much easier
LatinIME didn't have such a dependency.

This CL mechanically copies files in 'inputmethodcommon' repository to
'LatinIME' repository.  In theory there should be no behavior change.

Bug: 110741521
Test: tapas LatinIME && make -j
Change-Id: I3fabb038be9a944dcd9ef79ffcc89800a5f0bf5a