Use public APIs to instantiate InputMethodSubtype

This is a groundwork for subsequent CLs that are
supposed to improve default input method selection
logics.

Historically we have had a @hide constructor of
InputMethodSubtype. However, this contructor is
a bit obsolete because we can not specify some
parameters that were added in recent platform
releases. We should use InputMethodSubtypeBuilder
instead.

BUG: 17347871
Change-Id: I72ad79682a58344e14380eb20e26edf98aee37cd