Enforce adb shell DeviceConfig flags restrictions

Android 16 limits the DeviceConfig flags that can be written by
the shell user to those that have been allowlisted. Since a
large portion of tests adopt the shell user's permission identity
to modify DeviceConfig flags, this change would impact these tests,
and the flags modified during tests would need to be allowlisted.
The feature initially rolled out in logging mode to capture all
flags that need to be allowlisted; now that the allowlist has
been updated, this commit switches the feature to enforcing mode
to prevent the adb shell user from writing flags that have not
been allowlisted.

Bug: 364083026
Flag: android.security.protect_device_config_flags
Test: atest DeviceConfigApiTest
Change-Id: I376fa6a57685bf27d76b9ac48ab60bf440b384c1