Whitelist packages for user types

Creates a new SystemConfig xml entry which allows a device to whitelist
system packages to be installed on users when they are created, based on
the type of user.

System packages will be installed on users when they are created, or
during OTAs, based on this whitelist. The whitelist can be
enabled/disabled via a Config resource.

For any user type, system packages can be whitelisted or blacklisted.
If it is both (for the same user type), the blacklist takes priority.
If it is neither, it won't be installed (since it isn't whitelisted).

If a system package isn't mentioned in the whitelist file at all, for
any user, then its behaviour depends on the Config resource value, which
can optionally implicitly whitelist all such apps on all users.

For now, the list is mostly empty and the default config is set to be
enabled but implicitly whitelist all system packages that are not
mentioned.

Test: atest FrameworksServicesTests:SystemConfigTest
Test: atest com.android.server.pm.UserManagerServicePackageWhitelistTest
Test: manually test user 0 by flashall -w and checking packages
Test: manually test OTA by setting setprop persist.pm.mock-upgrade 1
Bug: 134605778

Change-Id: Ia098c1f597f66a1c946cfcc9b7771c25e8ceabf7