Language and variant selection for Minikin

This is the frameworks/base side of what's needed to support language
selection (especially Han unification, but also compact/elegant
selection for scripts that require more vertical space).

This is part of the fix for bug 15179652 "Japanese font isn't shown on
LMP".

Change-Id: I8f0f3aa9a1915659f8d0b590cf1c56529356049a