Flexiglass: Add border for keyguard pin input when keyboard is supported

Pre-flexiglass, we draw a customized background for the keyguard PIN
input field (in KeyguardPasswordViewController). This CL add the same
support for flexiglass by drawing a border in PinInputDisplay.

Bug: 413303961
Test: PinBouncerViewModelTest, manually verify through the keyguard
login screen when keyboard is connected
Flag: com.android.systemui.scene_container

Change-Id: Ic1fcacdc640447a8c120f332777ec7c21891f3e2