Allow vrmanager to connect to vr_window_manager.

The vrmanager system service connects to vr_window_manager to
provide access to controller data for 2d embedding. This is
intended to be removed when the relevant parts of vr_window_manager
are moved into VrCore (b/36506799).

Bug: 35619424
Test: manual on device
Change-Id: I9c645882bf1a14a85bbc4c2312164381b23aaa54