This patch adds a "lang" pseudo-CSS property and uses it both to select
an appropriate font and control the "locl" OpenType feature to get the
most appropriate rendering for the langauge and script.  In addition,
the "-minikin-variant" property selects between "compact" and "elegant"
variants of a font, as the former is needed for vertically cramped
spaces.

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

Change-Id: I7fab23c12d4c797a6d339a16e497b79a3afe9df1