CaptivePortal: implement setDelegateUid API.

This API is designed to set the UID of the app that is allowed to
perform network traffic for captive protal login, communication will
bypass network access restrictions such as VPNs and private DNS settings
when a portal page is launched by Android Custom Tabs and bind the
upcoming traffic to that portal network.

Bug: 373773542
Test: atest ConnectivityCoverageTests
Change-Id: I9992671634b8e88f5a647455811a6157fb15a44b
6 files changed