Rename getVpnRequiresValidation and getRequiresInternetValdiation

Update the API naming below to address API review feedback:
1. NetworkAgentConfig.getVpnRequiresValidation to
   NetworkAgentConfig.isVpnValidationRequired
2. PlatformVpnProfile.getRequiresInternetValdiation to
   PlatformVpnProfile.isInternetValidationRequired

Test: atest FrameworksNetTests
Bug: 220129160
Change-Id: I972c38c10f405bcb29f21d764d8480cb93fa68c1