Misc fixes to CryptKeeper

- use standard IME, but force it into ASCII if it's the default IME
- provide an IME switcher if there are multiple IME's, in case the
ASCII-capable one is a different one
- make the IME shown by default

Bug: 5004456
Bug: 4698473
Change-Id: Id40a164cfe599bfdb67b81f60d4ab8a52208de88