Add device config tests to GameManagerServiceTests

Refactors the tests to not use deprecated MockPackageManager
class and moves it into the mockingservicetests directory.

Adds tests to handle varying device configs for a package.

Simplifies DeviceConfig logic to use package names as keys
directly.

Bug: 183041877

Test: atest com.android.server.app.GameManagerServiceTests

Change-Id: I2e25b0dc77ef5255d3d3c5668122ab9a9f6348ba