AssetManager support for 3 letter lang/country codes.

- 3 letter codes are packed into the existing 32 bit locale
  field in ResTable_config
- We introduce new fields for script / variant information.

Note that we define a "match" between two ResTable_config
structures to be purely on the basis of their language &
country (disregarding the script and the variant). However,
configs with scripts and variants are considered to be more
specific than those without.

(cherry picked from commit 378c6775)

Change-Id: I7dce82a3fe2412834252723f458826ae41535a78