ChooseLockPassword: convert to use PasswordMetrics#validateCredential()

Fix the check for invalid characters in new passwords by switching from
PasswordMetrics#validatePassword() to
PasswordMetrics#validateCredential().  For more information, see
frameworks/base change I5c3c55367c3a294578cd0f97ac0e315a11ed517e.

Bug: 219511761
Bug: 232900169
Bug: 243881358
Test: Verified no regressions in 'atest ChooseLockPasswordTest'.  Note,
      this test is currently @Ignored and has 2 failures.  I didn't
      attempt to address that.
Test: Set a password containing non-ASCII characters on a device running
      an older build.  Upgraded and verified unlocking still works.
      Tested that setting a new non-ASCII password is not allowed.
Change-Id: I5f1822a34688473cb103eb64dca56e4c19d4dd08
Merged-In: I5f1822a34688473cb103eb64dca56e4c19d4dd08
(cherry picked from commit b5470943)