Update text when Active Unlock is enabled.

Update the security summary, intro, and unlock your phone summary when
Active Unlock is enabled and enrolled on the device.

Test: make RunSettingsRoboTests
Test: manually flip flags, confirm combined page has updated strings
Bug: 264812018
Change-Id: I2843e9f3aa0f38a9f2ebb18d60fed6293f9ce36e