Send keyguard category to widgets in GH

This informs widgets that they are being shown on the keyguard, so they
can adjust accordingly.

Fixes: 324600993
Test: atest SystemUiRoboTest:CommunalWidgetHostTest
Flag: ACONFIG com.android.systemui.communal_hub STAGING
Change-Id: Ied8fc683e780d3fc409b352f0a36b22d403eaa5c