Refactor helper method to return integer ranges.

Calls to setRequireVpnForUids() for Vpn lockdown actually uses a
List instead of a Set of integer ranges.
Add intRangesExcludingUids() to return the needed List of integer
ranges and replace relevant usages of UidRange.toIntRanges() with
it.

Bug: 230548427
Test: atest FrameworksNetTests
Change-Id: I61cd4751ce2faeb129daa5ad5da7181e3c1df73c