Conditionally include VCN in Tethering module

When the build system flag RELEASE_MOVE_VCN_TO_MAINLINE is true,
VCN framework lib will be included in the tethering boot classpath
fragment and the VCN service lib will be included in the
service-connectivity.jar

Bug: 375213246
Test: flag enabled: VCN libs are in the tethering module
      flag disabled: VCN libs are in the platform
Flag: RELEASE_MOVE_VCN_TO_MAINLINE
Change-Id: If0239eb1684b861b63794762915dab0d62379885
6 files changed