Implement temporary upper case hint icon

This change partially implements the requested feature. The following
are not supported yet.
- Non-letter key handling on automatic temporary upper case layout.
- Non-letter key handling on shift chording in caps lock layout.
- Hint icons for manual temporary upper case layout are not final ones.

Bug: 3193390

Change-Id: I636da99d1be05b1337935d87c6f4d140661e1cc8