Use Set to group Keys in Keyboard instead of List

In deriving various shift stated alphabet keyboards from base/main
keyboard, almost all keys should be shared among variants.  Grouping
keys in Set instead of List is a essential refactor to have.

Bug: 5002108
Bug: 5679585
Change-Id: Idd5644d1c45a3276a24b61c984619c03d4e4c54c
5 files changed
tree: da5ecf61a5a2635c8fcf40e073da6205cf27385a
  1. dictionaries/
  2. java/
  3. native/
  4. tests/
  5. tools/
  6. Android.mk
  7. CleanSpec.mk