Introduce script matching for enabling default IME subtypes.

This is 2nd attempt of I5bb1bd8cdb9096d516d60beb9936e55bf2b757ae

The motivation of this CL is enhance the default IME subtype enabling
algorithm.  The new approach is done by score based algorithm.  The
design of the matching score is determined as follows:
- The matching score for the each two locale is up to 3 and determined
  as follows:
  - Score of 3 : matches all language, script and country.
  - Score of 2 : matches the language and script.
  - Score of 1 : matches the language regardless of country.
  - Score of 0 : doesn't match the language regardless of script and
                 country.
- All locales are fully expanded before matching by addLikelySubtags in
  ICU.

Bug: 27129703
Bug: 27348943
Change-Id: I8fc774154f5175abff2f16e8f12a4847bf5f5b7c