Features and bugfixes targeted to coincide with WinGet 1.8

The "Due date" is aspirational and primarily intended to help sort Milestones.

As the date approaches, features and bugs may be moved to the next milestone.

Note: When new schema changes are released in the WinGet client, changes to support new manifest keys will not be rolled out for validation until more than 50% of devices have upgraded to the latest stable version of the client.