Changes for storing the PIN length

This CL aims at making changes for storing the PIN length in device
encrypted storage. This would happen in two places, one when user
successfuly unlocks the device and other when user is updating the PIN
on their device.

Test: Tested by building and flashing on local, and checking if PIN length is stored by printing the value using logcat. Disabled feature flag to make sure that if it's disabled, the PIN length isn't stored.
Bug: b/262929169
Change-Id: I1ea2b07688e1486f2ef47513218409b7f7fe4a7d