Update OemNetworkPreferences to use 1:1 Map

Updated OemNetworkPreferences to use a Map instead of an Array of Arrays
(SparseArray<List<String>>). This is for two reasons: to make the API
simpler and also prevent issues with duplicate entries for packages
mapped to more than one preference which is not supported.

Bug: 176597181
Bug: 176494815
Test: atest FrameworksNetTests
Change-Id: I85363e28b46b89ae60a85219313c2a45bd5e7dd5