The motivation of this CL is enhance the font fallback score design
to support multiple language font fallback.

This CL contains following changes:
- Break language based font score into two: script-based score and
  primary-language-based score.
- The primary-language-based score is 0 if the script-based score is 0.
  If the script-based score is not 0 and the primary language is the
  as same as the requested one, the font gets an extra score of 1.
- The language score gets a higher multiplier for languages higher in
  the locale list.

Bug: 25122318
Bug: 26168983
Change-Id: Ib999997a88e6977e341f4c325e2a1b41a59db2d5