Pull VcnNetworkProvider out into a separate class

This change makes the VcnNetworkProvider a separate class, and caches
all NetworkRequest(s) to ensure that VcnTunnel(s) satisfy all requests
that they can accept.

Bug: 163431879
Test: atest FrameworksVcnTests
Change-Id: I3b7695628d0153a33f7e7f40d839df1463d58b07
7 files changed