IcuCollation: Add CollationCkb subclass for Sorani Kurdish

ICU does not currently support Sorani Kurdish / Central Kurdish
language ('ckb'). CollationCkb uses the same collation rules as
Persian / Farsi ('fa'), but different characters for digits.

For use at ckb.wikipedia, which currently has 'uca-fa' collation
deployed as a workaround.

Added the MW language used for transforming digits to cache key for
first-letters data, in addition to the ICU locale.

Bug: 55630
Change-Id: I7d7f007592ede952859c5c9556b9ea5084b90e89