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.

Change-Id: I3c2e909ebbebdbbd0ab72a639d531b2b9fdbd9b9