Update strings for choose lock password/pattern screen

Makes the following changes to the header/description text shown on the
choose lock screen:
- Remove references to "biometrics" in favor of "face or fingerprint"
- Add a default description when setting a PIN/pattern/password

Test: Manual

Bug: 191923052
Change-Id: I788fd03aaeea624fab548d1c055c5c6dee076e2d