Check network slicing declaration for network request

When the application wants to request network with
NET_CAPABILITY_PRIORITIZE_BANDWIDTH or
NET_CAPABILITY_PRIORITIZE_LATENCY, it has to declare
PackageManager.PROPERTY_NETWORK_SLICE_DECLARATIONS property and also
adds the declaration in a separate XML files. Otherwise, the request
will fail with a SecurityException being thrown.

Test: atest FrameworksNetTests CtsNetTestCases
Bug: 266524688
Change-Id: I6affc857b803211517368da288e1b2fdc06a955b