Simple numbering system selector for LocalePicker.

This change introduces minimal changes needed to support selection
of locales with BCP 47 numbering system specification. Two level
selection (Language/Region) schema remains, locales with numbering
systems appear in the region selection list and are displayed as
"region (numbering system)".

Bug: 18340949
Bug: 63754513
Test: manual, experimental UI for review.

Change-Id: I42691f3714c5e5c51fd8d96c034cc3a9f6be93dc