Disable Call Forwarding option "When Unreachable" if configured

Read carrier config KEY_CALL_FORWARDING_WHEN_UNREACHABLE_SUPPORTED_BOOL.
Call Forwarding option "When Unreachable" in Call settings will be
disabled and greyed out if false.

This prevents unnecessary signaling for carriers where this option is
not supported by the network and prevents error dialog from being
displayed to the user.

Bug: 118861990
Test: atest TeleServiceTests
Change-Id: I9b03d7543572f8ba5482c7e6242d2ebd4617e5c5
1 file changed