Confirmation dialog for opening NFC-scanned urls

This adds an confirmation dialog displayed before opening an url from a
scanned NFC tag. The feature is off by default for now and will be
selectively enabled via a build overlay, but we plan to turn this on
unconditionally in the future.

Bug: 30109939
Test: manual
Change-Id: I3884fd9b7a492504afa86e75c55fced0741de8e1
4 files changed