Create VCN folder

This is a preparation CL to decouple VCN from the platform code.
It follow the steps suggested by go/mainline-onboarding-in-trunk-stable.
Eventually VCN will be moved to Tethering module. Followup CLs will
migrate all VCN source code to this folder and thus VCN will not
automatically be built into the framework.jar and services.jar anymore.

Bug: 369703242
Test: build and boot
Flag: EXEMPT no functional change
Change-Id: I41484406ab88a8910a87f8df9e53199731c0ce08