Introduce LockscreenCredential

* Wrap credential bytes and type into one single object.

* Update all external APIs dealing with lockscreen passoword
  to use the LockscreenCredential class. Remove existing variants
  that handles pin/password/pattern separately.

* Coerce password quality passed to LockSettingsService into one
  of UNSPECIFIED, PATTERN, NUMERIC or ALPHABETIC (explained below).

* Update all clients & tests to interface with LockscreenCredential.

Note: LockscreenCredential distinguishes between PIN and password
in its public interfaces, this is to pave the way for the next
patch of formally introducing a CREDENTIAL_TYPE_PIN type and
getting rid of the requestedQuality being passed along (whose
sole purpose nowadays is to distinguish between PIN and password)
For now LockscreenCredential still uses the quality value internally
to make that distinction. This does result in a change to what
quality values LockSettingsService receives as part of credential
change: after this CL LSS will only see the quality being
one of UNSPECIFIED, PATTERN, NUMERIC or ALPHABETIC, while it used to
receive other qualities (NUMERIC_COMPLEX, ALPHANUMERIC etc) if device
admin sets a password policy. This shouldn't make any behaviour changes
though, because the new range of values is still sufficient to
distinguish between PIN/Pattern/Password, which is what the consumers
of the stored quality care about.

Bug: 65239740
Test: atest com.android.server.locksettings
Test: atest com.android.server.devicepolicy.DevicePolicyManagerTest
Test: atest com.android.internal.widget.LockPatternUtilsTest
Test: atest com.android.internal.widget.LockscreenCredentialTest
Test: make RunSettingsRoboTests ROBOTEST_FILTER=com.android.settings.password
Test: atest MixedManagedProfileOwnerTest#testResetPasswordWithToken
Test: atest MixedDeviceOwnerTest#testResetPasswordWithToken
Test: manually set an PIN/Pattern/Password; then change to
      PIN/Pattern/Password; finally remove password
Test: manually create a work profile; try unify and ununify work
      challenge.
Test: manually test lockscreen FRP flow (change password via Settings /
DPC)
Change-Id: I04cc04057c96292a7b1b672bff2a09d594ea9b3c