Added API to replace unicoded digits to ascii numbers

Users can enter arabic phone number or click arabic phone number
to send MMS. Works for generic Unicode digits (full-width, etc.).

bug:5615791
Change-Id: Ieec8c5c6c3736ee2b4ac8ddf17f8c41b2001460e

Signed-off-by: Jake Hamby <jhamby@google.com>