Manage controller connection from VrCore to VrWindowManager.

Use VrManager as a proxy to pass the controller data file descriptor
from VrCore to VrWindowManager, since the latter is a purely native
service with no Java visibility.

This is intended to be replaced by moving the relevant parts of
VrWindowManager into VrCore (b/36506799).

Bug: 35619424
Test: manual on device
Change-Id: I9545349893ed9b23de4ba8d3cb61c7d403ad0b97