vkr: only tear down the vk obj tree for threaded render worker
vkr must still cleanup the vkr allocated bits upon teardown, and now the teardown looks like:
- context teardown
- cleanup all vkr allocs at context/instance/device/sub-device levels
- do not destroy vk instance or device or other device level objs created by the app
- instance teardown
- cleanup all vkr allocs at instance/device/sub-device levels
- do not destroy vk device or other device level objs created by the app
- device teardown
- cleanup all vkr allocs at device/sub-device levels
- do not destroy other device level objs created by the app
The exception is threaded render worker config to avoid leak in the server process to help debug. Thus no behavior change here.
Do it in the way that the code path always gets compiled.
/cc @dawnhan