Support exclusion widget category filter in the widget picker

The newly added NOT_KEYGUARD category enables hosts that shows all
widgets to let widgets opt out from being displayed in keyguard like
surfaces.

Bug: 394047125
Test: Unit tests and support app
Flag: EXEMPT bugfix

Change-Id: Ibaab0c8a052700b77289cd571bca33e3d96fa09f
3 files changed