Wipe the LockscreenCredential in DPMS#resetPasswordInternal

This CL adds try-with-resources around LockscreenCredential objects,
in order to call `close()` when the resource is done being used.
This also clears the LSKF `byte[]` representation in the LockscreenCredential.

This CL applies the above changes to the DevicePolicyManagerService.

Bug: 320392352
Test: build
Change-Id: Iad642dd4706ae052affc2f9ac6d6f0695870728d