Move all bouncer strings to a helper class that can be reused by both legacy and flexiglass implementations.

Other changes:
 - Change the unattended update message in the new implementation
 - Also update the message text to "Pin/pattern/password required for
   additional security"

Bug: 299343534
Test: NA
Flag: ACONFIG com.android.systemui.revamped_bouncer_messages TRUNKFOOD
Change-Id: I818b17c793649b54ff3845cdf327a87cb4d877a6
7 files changed