Add the ability to provide default values to the following static A2UI

property types: enums, numbers, booleans.

These are required to implement the basic catalog spec.

Bug: 547851648
Test: A2uiPropertyTest
Relnote: """Added `default` parameters to the enum, number, and boolean
    `A2uiProperty` types."""
Change-Id: Id509ea0050b3e3a0e075057ea56683727fe72f3d