Improve wear keyguard unlock by prioritizing `checkCredential`

High unlock times have been observed on wear devices specifically.
b/403536398 identified that the low priority of the `checkCredential`
method contributes to this issue.

This change increases the priority of the `checkCredential` method to
`THREAD_FOREGROUND` (priority 118). This priority level was chosen
based on testing in b/403536398, which demonstrated the best performance
gains.

Flag: com.android.internal.widget.flags.run_check_credential_with_higher_priority
Test: m
Bug:407716215
Change-Id: I1c01bdbe9121a4d7e49ea5223ed6d82bc787654b