Enrich test cases when enabling default IMEs part 3

This is another groundwork for subsequent fixes.

Notable changes in test cases are:
- A dummy Hinglish IME ("en_US" + "hi") is added
- Added test cases where system locale is "en_GB",
  "en_IN", and "hi" as well as "en_US".

BUG: 17347871
Change-Id: Iacf0f47c4dbc147f8153df50ba58fc4da4dacd29