Stop saving password metrics to disk

Previously, DevicePolicyManager saved password stats (number of letters,
number of symbols, etc) to disk for FDE devices. This made it possible
for the isActivePasswordSufficient() API to return a result before the
password was entered for the first time after a reboot. Access to these
stats would significantly narrow the space of possible passwords an
attacker would need to explore.

Going forward, every time either the password or the password
requirements change, a flag will be persisted indicating whether the
current password meets the requirements. Before the password is entered
for the first time after a reboot, isActivePasswordSufficient() simply
returns the value of this flag. (After the password is entered for the
first time, isActivePasswordSufficient() uses password stats saved in
memory, as is the case today.)

This creates a window where isActivePasswordSufficient() may return an
incorrect value before the password is entered for the first time, if
the requirements are changed after startup so that the current password
no longer meets the requirements. This has been deemed an acceptable
compromise in order to avoid storing potentially sensitive data.

Test: runtest -c com.android.server.devicepolicy.DevicePolicyManagerTest
frameworks-services

Bug: 34218769
Change-Id: I5d3cd008a9ee2787bcb10ed5455bb61c6014ae00