Give hidden API behavior to legacy apps.

Starting in R, there is a new public API overload that delivers a
flags argument.  Some apps may be relying on a previous hidden API
that delivered a userId argument, and this change is used to control
delivery of the new flags argument in its place.

There are dozens of these hidden API users are in the system UID,
either in the system process or the Settings app, so we hard-code
giving them the legacy behavior, since refactoring would be messy
between internal and AOSP branches.

Also adjust incoming and outgoing method signatures to use slightly
more flexible Collection<Uri>, which has handy methods like
contains() and isEmpty().

Bug: 150939131
Test: atest --test-mapping packages/providers/MediaProvider
Test: atest FrameworksServicesTests:com.android.server.devicepolicy.DevicePolicyManagerTest
Exempt-From-Owner-Approval: trivial refactoring
Change-Id: If6a77449e19215cf1c60d4217e62fc04b0959bfc